A practical treatise on mechanical dentistry

Front matter

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K . B. rmui

Preface To Second Edition

The exhaustion of a large edition of the present work under circumstances which have, in a marked degree, affected the sale of all similar publications adversely within the past eight years, and the assurance of its favorable acceptance by the profession, conveyed in the various friendly, impartial, and generally commendatory notices which greeted its first appearance, afford adequate encouragement for the preparation of a second edition, which, it is hoped, will, in a still greater degree, commend itself to the favorable consideration of the profession.

Aiming, in the first instance, to make this treatise a distinctly practical guide to the manipulations of the dental laboratory, discarding everything, in point of facts or modes of practice, which was not well grounded in theory and confirmed by experience, the Author finds but little embraced in the first, which it is deemed necessary to exclude from the second, edition. Some verbal corrections and changes of phraseology have been made, and numerous interpolations and additions of matter introduced throughout the body of the work, while other portions have been almost entirely re-written.

The chapter on Vulcanite Base has been so revised and . extended as to comprehend all that is valuable and approved

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Preface

in tliat particular process, and will, it is believed, be found to be as comprehensive and reliable in text and illustration as any description of the method yet published.

In the initial portion of the chapter devoted to Artificial Dentures with Continuous Gums, the practitioner and student will be gratified to find descriptions of this unrivalled process from the pen of its distinguished Author himself, embracing a concise and intelligible account of the various modes of procedure employed at this time by Dr. Allen.

The Author’s special and grateful acknowledgments are due to Prof. Norman W. Kingsley for the able, comj)rehensive, and highly instructive contribution on Artificial Vela and Palates, which appears at the close of the volume. The accompanying illustrations, explanatory of the text, derive additional value from having been executed under his own immediate supervision, and will, it is believed, convey a more satisfactory and intelligible understanding of the mechanism of the apparata employed by him, than any heretofore imparted by published descriptions.

An additional chapter has been embodied in the work, embracing all the information of a practical character that could be obtained in reference to the working of Aluminium as a base for artificial teeth. •

Processes in a stage of but partial or incomplete development have not been treated of for the reason that it is

judged inconsistent with the design and character of a work like the present to embrace descriptions of immatured methods or modes of manipulation, the practicability of which has not been ascertained, or the merits of which have not been passed upon or confirmed by the common experi-

PREFACE.

IX ence of the profession. Time must be given to sanction or condemn whatever does not at present stand approved.

In the preparation of the present, as in the former, edition, the Author has not hesitated to appropriate whatever was deemed valuable and approved from all the sources at his command, but he has aimed, in every instance where the results of the labors and experience of others have been embodied, to accord the proper credit. For the many personal favors and courtesies generously extended to him by individual members of the profession, his thanks are, in an especial manner, due.

Preface To First Edition

In tlie prep-aration of the following treatise, the author has endeavored to present, in as concise and methodical a form as possible, the material facts and principles which relate to the Mechanical Department of Dental Practice in its present advanced condition. In the accomplishment of this undertaking, the primary and leading purpose has been to furnish the student and more inexperienced practitioner with a practical guide to the manipulations of the laboratory, with accompanying elucidations of the elementary principles which underlie the practice of this important specialty. In furtherance of this design, all matters, discussions and commentaries not strictly material, have been carefully excluded.

The arrangement and treatment of the various subjects •embraced are such, it is believed, as will best facilitate the student in the acquisition of a knowledge of the department alluded to, and the practitioner in the intelligent and successful conduction of the manipulations which appertain to this branch of Practical Dentistry.

In the belief that these objects have been mainly accomplished, the work is respectfully submitted to the profession.

J. PlCHARDSON.

CincinnatL

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Dedication,

Preface,

PAGE

V

VII

Part First

METALS EMPLOYED IN DENTAL LABORATORY OPERATIONS, WITH PRELIMINARY OBSERVATIONS ON THE DIFFERENT MODES OF APPLYING HEAT.

Chapter I. Page

Different Modes of Applying Heat 25-45

Blowpipe, 23

Mouth Blowpipe, 26

Bellows Blowpipe, 29

Self-acting or Spirit Blowpipe, 30

Hydrostatic Blowpipe, 32

Lamps, 37

Oil Lamp 37

Spirit Lamp, 37

Furnaces, 38

Draft or Wind Furnace 38

Baking Furnace, 40

Fuel, 41

Supports, 44

Crucibles, 45

CHAPTER IV. Reducing Metals, 60

Required fineness of Gold Plate, 60

Formulas for Gold Plate used as a Base for Artificial Dentures, . . 61

Formulas for Gold Plate used for Clasps, Wire, Stays, Metallic Pivots, &c., 63

Gold Solders 64

Method of reducing Gold to a lower or higher standard of fineness, and of

determining the caret of any given alloy^ 65

Table of Gold Coinage of different Nations, 69

CHAPTER V. Method of converting Gold Alloys into the required forms for

DENTAL purposes 74-80

Manner of procuring an Ingot, 74

Forging, 75

Laminating or Rolling, 75

Thickness of Gold Plate required as a Base for Artificial Dentures, . 77

Thickness of plate for Clasps, Stays, &c., 78

Reduction of Gold Solders into proper forms for use, .... 78

Method of obtaining Gold Wire, 78

Method of constructing Spiral Springs, 80

CHAPTER I. Treatment of the mouth preparatory to the insertion of

ARTIFICIAL DENTURES, 102-110

Useless and diseased remains of teeth, 103

Removal of salivary calculus or tartar, ...... 106

Diseased conditions of the mucous membrane and gums, . . . 107

Caries or decay of the remaining teeth, ...... 107

Surgical treatment of the mouth after the extraction of teeth, . . 107

Time necessary to elapse after the extraction of teeth before in.serting artificial dentures, 108

CHAPTER II. Materials and methods employed in obtaining impressions of

Manner of obtaining an impression of the mouth in wax for partial upper dentures, 112

XVI

CONTENTS.

PAOE

Manner of obtaining an impression of the lower jaw in wax for partial dentures, 115

Manner of obtaining an impression of the mouth in wax for entire

upper dentures, 115

Manner of obtaining an impression of the lower jaw in wax for entire

dentures 118

Gutta-percha, 119

Plaster of Paris, . - . 119

Manner of obtaining an impression of the mouth in plaster for partial

upper dentures, 121

Manner of obtaining an impression of the mouth in plaster for entire

upper dentures, 123

Manner of obtaining an impression of the mouth in plaster for entire lower dentures, 125

CHAPTER III. Manner of obtaining a plaster model from an impression in wax for

Manner of obtaining a plaster model from an impression in wax for

Manner of obtaining a plaster model from an impression in plaster for

Manner of obtaining a plaster model from an impression in plaster for entire dentures, . . . 133

CHAPTER IV. Manner of obtaining a Metallic Die, 134

Molding, 134

Dipping, 140

Counter-Die, 141

Essential Properties of a Die, 142

Table of Fusible Alloys, 148

Chapter V

Means employed in retaining partial sets of teeth in the mouth, . . 150

Circumstances modifying the success of the operation, . . . 151

CONTENTS.

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PAOB

The roots of teeth to which artificial crowns are usually attached, . 153

Preparation of the root, 153

Fitting the crown, 158

Attaching the crowns by means of wood pivots 159

Pivots of metal and wood, 152

Metal pivot, 162

Pivot plate 165

Substitution of rubber for wood pivot, 167

Wired rubber pivot, with rubber base, 167

Canal of root lined with rubber tube for the reception of gold pivot

vulcanized into a crown, with rubber base, 169

Substitution of a plate for a pivot tooth, 170

Chapter VI. •

Partial dentures retained in the mouth by means of clasps attached TO THE NATURAL TEETH, 173-193

Remarks on the use of clasps 173

The teeth to which it is most proper to attach clasps, .... 175

^ Separation of the teeth, by filing, for the reception of clasps, . . 177

Modifications in the form of clasps, 178

Modifications in the form of plates for partial dentures supported in

the mouth by clasps, 182

Swaging or stamping the plate, 187

Uniting the plate and clasps, 190

Chapter XI

Method of constructing a plate base for an entire denture for the upper

Modifications in the form of plates for entire upper dentures, . . 223

Method of constructing a plate base for an entire denture for the under 228

Antagonizing model for an entire upper and lower denture, . . 229

Antagonizing model for an entire upper denture with the natural teeth

of the lower jaw remaining, 233

Selecting, arranging, and antagonizing the teeth ; rimming the plate ;

attaching spiral springs ; investing, lining, soldering, and finishing, 234

CHAPTER XII. Substances used in the manufacture of porcelain as applied to

dental purposes, 247-249

Felspar, ■ 247

Coloring materials, 249

CHAPTER XIII. Composition and preparation of the Body, 251

Composition and preparation of Crown Enamels, 252

Composition and preparation of Gum Enamels, 253

Antagonizing model for an entire upper and lower denture constructed

of block teeth 255

Antagonizing model for an entire upper denture with the natural teeth

of the opposing jaw remaining, 255

Forming a matrix for molding the body preparatory to carving the

Molding the porcelain paste preparatory to carving the teeth, . . 259

Carving the teeth, 262

CONTENTS. xix

PAGE

Crucing or Biscuiting 262

Application of the Crown and Gum Enamels, 263

Final Baking, 264

Fitting and attaching the blocks to the metallic base, .... 264

Dr. Calvert’s method, 266

Chapter XIV

Uniting single porcelain teeth to each other and to a metallic BASE WITH A FUSIBLE SILICIOUS COMPOUND, FORMING A CON- TINUOUS ARTIFICIAL GUM 271-293

Introductory remarks, 271

Dr. Allen’s Modes of Practice 275

Dr. Hunter’s Formulas and Modes of Practice 283

Application of Continuous Gum to Partial Sets, 290

CHAPTER XV. General Properties of India-rubber 294

Compounding Eubber for Dental Purposes, 295

Objections to the Use of Rubber Considered, 305

Method of Constructing an Entire Denture in a Base of Eubber, . 309

Arranging the Teeth, 310

Formation of the Mold or Matrix, 312

Packing the Mold, 317

Vulcanizing, 325

■Finishing, 338

Partial Dentures Constructed in a Base of Rubber, .... 339

Metallic Clasps attached to Rubber Plates, 341

Substitution of Plate for Rubber Teeth, 342

Repairing, 342

Refitting Gold or Rubber Plates with Rubber Lining 343

Attaching Porcelain Teeth to a Metallic Base by means of Rubber, . 346

Manner of obtaining an exact Duplicate of a Set of Teeth on Rubber, 349

CHAPTER XVI. Cheoplastic method of mounting artificial teeth, . . . 352-359

Method of Constructing Entire and Partial Dentures in a Base of

Cheoplastic Metal, 352

Finishing 353

Repairing, 353

XX

CONTENTS.

PAGE

CHAPTER XVII. Aluminium Plate Base, 360

Aluminium Solder 362

Cast Aluminium Base, 362

Dr Bean's Method, 363

Preparing the Expanded Mold and Casting the Matrix, . . . 363

Constructing the Model Set, 377

Investment in the Flask and Completion of the Mold, . . . 383

Casting the Plate 389

Finishing the Plate, 392

Securing the Teeth to the Plate, 397

Casting Shells for Lower Sets, 402

Repairing Aluminium Work, ........ 405

Casting Lower Sets of Tin and Silver, 406

Mending Defects in Aluminium Plates, 409

Refining Aluminium Scraps and Dross, 411

Alloys of Aluminium, 412

Preparation of the Alloy of Silver and Tin, ' 413

Chapter XVIII

Defects op the palatal organs and their treatment by artificial MEANS, 414-435

Palatine Defects, 414

Obturators, 415

Artificial Palates, 418

Artificial Palates for Congenital Fissure, 424

Method of making an Artificial Palate, 427

MECHANICAL DENTISTRY.

Part First

METALS EMPLOYED IN DENTAL LABORATORY OPERATIONS, WITH PRELIMINARY OBSERVATIONS ON THE DIF- FERENT MODES OF APPLYING HEAT.

Chapter I. Different Modes Of Applying Heat

The application of heat to the various mechanical processes of the dental laboratory would seem to require a brief description of some of the agencies employed for the purpose. As full a description of the appliances used will be introduced as is compatible with the scope of the present work.

BLOWPIPE.

Various modifications in the form of the blowpipe have been introduced from time to time, and are named according to the means used to produce the blast, as. Mouth, Bellows, ' Self-acting or Spirit, and Hydrostatic Blowpipe.

In addition to the varieties mentioned, there are others used in producing extreme degrees of heat, as the ^‘oxygen blowpipe" with which the flame is blown with a jet of oxygen; and another, with which the two gases, oxygen and hydrogen, 3

MECHANICAL DENTISTRY.

are burned, called the oxy -hydrogen blowpipe." The latter is capable of producing a heat that immediately fuses the most refractory substances, as quartz, flint, rock-crj-stal, plumbago, &c. With it, gold is volatilized, and iron rapidly consumed when placed in the flame; while platinum, next to iridium, the most infusible of all known metals, has been melted in quantities exceeding one hundred ounces by means of this powerful instrument. As, however, these blowpipes are of no special practical utility in the dental laboratory, any further reference to them will be omitted.

Mouth Blowpipe. — This instrument has been long in use, is simple in its form and construction, and, for general use in the application of moderate degrees of heat, is both convenient and economical. Those accustomed to its use are enabled to produce a continuous blast of considerable force, and soon acquire the facility of regulating the heat produced with equal if not greater precision than can be readily attained in the use of either of the other varieties mentioned.

The most simple form of the mouth blowpipe is shown in Fig. 1. It consists usually of a plain tube of brass, larger at the end applied to the mouth, and tapering gradually to a point at its other extremity, the latter being curved and

Fig. 1.

tipped at the point with a conical-shaped, raised margin to protect it from the action of the flame : the calibre of the instrument terminates here in a very small orifice. The point of the instrument,* as well as that part of it received into the mouth, is sometimes plated with a less oxydable metal than brass, as silver or j)latinum. The stem is generally from twelve to twenty inches in length, and the mouth extremity from one-half to three-fourths of an inch in diameter.

MOUTH BLOWPIPE.

In operations requiring protracted blowing, a somewhat different form of the instrument will be required, owing to the accumulation of moisture within the tube, which, being forcibly expelled from the orifice, spirts upon whatever is being heated and interrupts the blast ; also, on account of the fatigue which in process of time renders the muscles of the mouth and face engaged in the act to a great extent powerless.

The difficulties mentioned may be obviated, in a great measure, by applying the form of blowpipe represented in Fig. 2. To the mouth extremity is attached a circular concave flange or collar which receives and supports the lips. To the shaft, near its curved extremity, is adjusted either a spherical or

Fig. 2 cylindrical chamber which collects and retains the moisture as it forms within the pipe. By allowing that part of the tube connected with the curved end to pass part way into the chamber, a basin is formed at the depending portion of the latter, which, by collecting the fluids, will effectually prevent them from overflowing and passing into the tube beyond.

There are other modifications of the mouth blowpipe somewhat allied in form to the one last described, but as they are constructed more especially for chemical examinations or analyses, and as they possess no advantages for dental purposes over those already mentioned, a description of them is not deemed necessary.

Mechanism involved in the act of producing a continuous blast with the mouth blowpipe. — As a steady, continuous current of air from the blowpipe is preferable to the interrupted

MECHANICAL DENTISTRY.

jet, in all those operations where it is desired to produce a steadily augmenting heat, the following remarks, explanatory of the method of producing it, are subjoined in the belief that they will render easier a process not always readily acquired.

“ The tongue must be applied to the roof of the mouth, so as to interrupt the communication between the passage of the nostrils and the mouth. The operator now fills his mouth with air, which is to be passed through the p^pe by compressing the muscles of the cheeks, while he breathes through the nostrils, and uses the palate as a valve. When the mouth becomes nearly empty, it is replenished by the lungs in an instant, while the tongue is momentarily withdrawn from the roof of the mouth. The stream of air can be continued for a long time without the least fatigue or injury to the lungs. The easier way for the student to accustom himself to the use of the blowpipe, is first to learn to fill the mouth with air, and while the lips are kept firmly closed to breathe freely through the nostrils. Having effected this much, he may introduce the mouth-piece of the blowpipe between his lips. By inflating the cheeks, and breathing through the nostrils, he will soon learn to use the instrument without the least fatigue. The air is forced through the tube against the flame by the action of the muscles of the cheek, while he continues to breathe without interruption through the nostrils. Having become acquainted with this process, it only requires some practice to produce a steady jet of flame. A defect in the nature of the combustible used, as bad oil, such as fish oil, or oil thickened by long standing or by dirt, dirty cotton-wick, or an un trimmed one, or a dirty wick-holder, or a want of steadiness of the hand that holds the blowpipe, will prevent a steady jet of flame. But, frequently, the fault lies in the orifice of the jet, or too small a hole, or its partial stoppage by dirt, which will prevent a steady jet of air and lead to difficulty. With a good blowpipe, the air projects the entire flame, forming a horizontal, blue cone of flame, which con-

BELLOWS BLOWPIPE.

verges to a point at about an inch from the wick, with a larger, longer, and more luminous flame enveloping it, and terminating to a point beyond that of the blue flame.”* Bellows Blo'^i'pi'pe. — This form of blowpipe, although superseded in a great degree by other modiflcations more recently introduced, is well adapted to all the minor operations of the shop, provided it is so constructed as to produce a continuous and equable current of air. A very efiicient form of this apparatus, contrived by Drs. McDaniels and Koudebush, is exhibited in Fig. 3. It consists of three distinct chambers; two lower ones, separated from each other in the centre, and one above, communicating by valvular openings with the former.

The basement boards of tbe lower compartments are accurately joined to each other in the centre with an inclination like that of an ordinary roof; are each about six inches square and have apertures in the centre with valves opening upward. The upper borders of these chambers are formed by the treadle or foot-board, consisting of a plain board, equal in length and breadth to both chambers, and adjusted by means of hinges to the basement pieces where they unite in the middle; — strips of India rubber cloth being glued along the joints on either side to prevent the escape of air from one chamber into the other. The upper chamber is*formed from a strip of board of equal length and half the breadth of the treadle, the ends and sides being closed, as also the lower apartments, with pieces of leather so arranged as to admit of expansion and closure of the air chambers. The lower chambers communicate with the upper or receiving chamber by means of an aperture in the top of each of the former with valves opening into the receiver.

* “ The Practical use of the Blowpipe.” Anon.

MECHANICAL DENTISTRY.

The movable top of the upper chamber should be bound down with compressed spiral wires arranged internally, or by strips of India rubber tacked to the borders of the chamber externally so that when the lid of the latter is forced open by the injection of air from the lower chambers, a steady compression of the contained air will be made, forcing it with a steady and continuous impulse into the rubber tube connected with the receiver ; i\\Q force of the current being regulated by the power exerted in depressing either end of .the treadle with the foot.

The modus operandi of this blowpipe when in use is briefly as follows : One end of the treadle being forced down, the contained air of the corresponding chamber underneath is urged through the valvular opening above into the receiver, while the air at the same time rushes in through the opening in the bottom of th>e opposite chamber, filling the latter : the other end of the treadle being pressed down, the air in the chamber below is, in like manner, also thrown into the receiver through the opening on the same side above ; thus, by an alternate action of the treadle, the receiving chamber is kept constantly replenished.

Self-acting or Spirit Blowpipe. — With this instrument the flame is blown with a vapor of boiling alcohol or whiskey. Several varieties have been introduced within the past few years, some of which are well adapted to dental laboratory operations, while others, owing to too great a complexity of mechanism in their construction, by which their action is rendered uncertain and liable to frequent and perplexing interruptions, have not been generally «^dopted ; others, again, are regarded as too unsafe and inconvenient for laboratory uses.

One of the best implements of the kind, simple in its contruction and design, and at the same time safe, convenient and manageable, is what is known as “ Hollely’s Self-acting or Spirit Blowpipe.” A description of this apparatus will serve to convey a sufficiently distinct idea of the prin-

SELF-ACTING OR SPIRIT BLOWPIPE.

ciple involved in the various modifications of the blowpipe under consideration.

The accompanying cut, Fig. 4, exhibits the different parts in their proper relation when in use. It consists of a cylindrical boiler, usually of brass, with a square-capped safety valve on top, so arranged as not to admit of complete closure, thereby rendering an explosion of the boiler impossible. The pressure of the contained vapor, and, by consequence, the

Fio. 4.

power of the jet may be increased by turning the thumb-screw connected with the valve forward, and lessened by a reverse movement of the same. The valve fixture may be removed by unscrewing it, and alcohol introduced into the boiler through the opening ; the boiler being from one-half to two-thirds full when in use. To the top of the latter near the side two pipes are attached communicating with the interior of the boiler, and which are provided with a gauge-cock, by which the operator is enabled, by a partial rotary movement of a thumb-screw, to control, somewhat, the force of the vapor current through the pipes, and also to transfer the jet from one pipe to the other, as he may desire a pointed or spreading flame ; or a commingling jet from both pipes may be simultaneously produced whenever a very large and diverging flame is required.

MECHANICAL DENTISTEY.

A small alcohol lamp being lighted, is placed underneath the boiler, when, after the lapse of a few minutes, a current of vapor will be forcibly expelled from the orifices of the pipes, and may be directed against the flame of any of the lamps in common use for heating purposes.

A blowpipe like the foregoing will be found serviceable in all operations requiring a protracted blast, and, in common with the bellows and hydrostatic blowpipes, will be found of especial service to those whose eyes and lungs are injuriously affected, as they sometimes are, by the use of the mouth blowpipe. It is also portable, as the various parts of which it is composed may be readily detached and packed within a small

Fig. 5.

space.

Hydrostatic Blowpipe. — This blowpipe is of comparatively modern origin, and for many purposes in the dental laboratory is the best that has yet been introduced. With it, a

constant, equable, and forcible current of air may be produced and maintained for a length of time equal to the capacity of the water-chamber ; and for all operations requiring a high and steady heat it is invaluable.

Fig. 5 represents an apparatus of this kind, which is so simple and economical in its construction, that every dentist may, with little trouble and at a trifling cost, provide one for his laboratory.

By reference to the annexed illustration, it wffll be seen to consist of a tank or cylinder made of sheet-iron, zinc or copper, of variable dimensions, usually, however, from four to six feet in length and from twelve to twenty inches in diameter. To the side of the

Tlf

HYDROSTATIC BLOWPIPE.

cylinder near the bottom a pipe with faucet is attached, called the “supply pipe,” and is designed to convey water to the tank ; another is attached to the bottom, termed the “waste pipe,” and is used to discharge the contained water. To the centre of the top of the cylinder is adjusted a stop-cock to freely admit the ingress of air when the water is being discharged, without which the sides of the cylinder would tend to collapse on the formation of a vacuum within. An India rubber tube is also united to the top of the cylinder on one side, and is attached at its other end either to an ordinary mouth blowpipe or gas jet.

The water being admitted to the tank through the supply pipe, the contained air is compressed and forcibly expelled through the air-tube and orifice of the blowpipe upon the flame; the force of the jet being regulated by the stop-cock connected with the supply-pipe. When the cylinder becomes filled, or partially so, the faucet on the top should be opened and the water drawn off" through the discharging pipe. A small glass tube, communicating with the interior of the cylinder on one side near the bottom, extending up the side, and again entering the cylinder at the top, will be found useful as a guide to determine, at any time, the depth of water in the tank, the water in the tube maintaining the same level with that in the former.

Those unable to command the facilities afforded by water power, may avail themselves of the following contrivance which combines mainly all the advantages of the blowpipe just described. A cylinder of the form mentioned, but with an open top, is partially filled with water, and another, similiarly formed but inverted, or with its closed end above, is made to fit and slide into the first. Weights are then placed on the top of the inverted tank, when the air within the latter will be forcibly compressed and impelled, as in the other case, through an air-tube attached to its upper closed extremity.

MECHANICAL DENTISTRY.

The following description of a hydrostatic blowpipe, (Fig.

6,)* of simple but ingenious construction is given by Prof. C. A.

Kingsbury, in the March (1864) No. of the Dental Cosmos, and which he affirms, after extended experience in its use, is “one of the most simple and effective I have ever seen where a stationary blow pipe is needed for the dental laboratory.”

“ A, represents a front view of a zinc or copper tank 20 inches high, 15 inches long, and 8 inches wide. B represents a side view ; and the dotted line between B and C a partition passing from within about an inch of the front upper angle down to within an inch of the lower back angle of the tank : or, in other words, this partition runs diagonally from the front upper angle to the lower back angle. This partition must be water tight, except at the bottom of the tank, where an open space is left of about an inch, so that when water is poured into the open compartment B — which is nearly as wide at the top as the tank is long — it can readily flow into the compartment C. When the tank is filled nearly half full it will be seen that the great bulk of the water will be in the front compartment C. The bellows is an ordinary large size house-bellows. The end of it rests upon the top of the

* The accompanying illustration was kindly furnished, at the instance of Prof. K., by Dr. S. S. White, for which and other similar favors the author would express his grateful acknowledgments.

HYDROSTATIC BLOWPIPE.

tank, and the handle of the bottom part is made, fast to an upright strip of board. A cord connected with the upper handle, having a weight of four or six pounds attached to the other end, passes over a small pulley for the purpose of raising the bellows. A cord connected with the same handle is attached to a small foot-lever or treadle, and by this means the bellows is easily worked with the left foot. To the nozzle of the bellows there is fastened one end of a plumber’s small brass joint; the other end of the joint is soldered to a piece of small-sized lead pipe which communicates with the compartment C at the top. In this brass joint is placed a leather valve — which any dentist of ordinary ingenuity can construct for himself — to prevent the air from returning back into the bellows. Connected with the lead pipe, running from the nozzle to the compartment C, is another piece (D), passing up through the work-bench or table, as the case may be, to which an old fashioned brass mouth blow-pipe is soldered. When the bellows is moved, the air is forced out of the pipe D and also into the compartment C, which becomes a reservoir for the air. For as the air presses down upon the surface of the water in C it is forced in the direction indicated by the arrow into the compartment B, which is open at the top. As the water is forced by the air in C into B its weight acts upon the air in C to drive it out of the pipe D, and in this way a steady and continuous blast, capable of being graduated to the wish of the operator by the greater or smaller quantity of water acting upon it, may be maintained with the most perfect ease. Any tinman can make the tank and its connections. Tin or zinc will do, but in the long run tinned copper would be the most economical. The apparatus should be placed at one end of the bench, or in some convenient place where it will not occupy much room.