Elementary chemical technics; a handbook of manipulation and experimentation for teachers of limited experience, and in schools where chemistry must be taught with limited appliances

Preface

The office of this little book is expressed in its title. My faith that such a work may be of some service in the cause of science teaching, is founded in part upon a realization of what a valuable adjunct such a book would have been in the earlier years of my own teaching.

No attempt has been made to write a text-book of Chemistry. There are enough good works of that nature to meet the requirements of every school. But from a proper regard for brevity, and sometimes from a lack of appreciation of the teacher's needs on the part of authors, text-books fail to give that careful detail of direction which will insure success in experimentation.

In the chapter on the Metals I have made no mention of the more rare ones, considering only such as are likely to be worked with in the ordinary school courses.

The terms of both the English and Metric systems are used, for I find that the two systems are used about equally in schools, and the tables provided in text-books render the conversion from one system to the other an easy matter.

IV PREFACE.

I wish to express my indebtedness to Prof. A. C. Boyden of the Bridgewater Normal, and to Mr. H. W. Tyler of the Massachusetts Institute of Technology, who have read the manuscript and proof-sheets, and given me valuable suggestions in my work.

GEORGE N. CROSS.

Spectrum Analysis 100

CHAPTER Xn.

Electricity in Chemical Reactions .... 104

ELEMENTARY CHEMICAL TECHNICS.

Chapter I. Construction And Equipment Of Laboratories

1. An apartment devoted exclusively to the purpose is not only a great convenience, but an absolute necessity, in the successful teaching of Chemistry. Neatness, convenience, health of pupils and teachers, the risk of injury to physical and other kinds of apparatus, and to school furniture from the use of chemicals in ordinary schoolrooms, and an encouraging degree of success in experimentation, all demand such a room in every school where Chemistry is taught.

2. Selection of Rooms. — Rooms upon the highest floor of a school-building possess some advantages in the way of ventilation, without the danger of vitiating the air of apartments above. But ground-floors and basements oftener furnish the desired accommodations.

The apartment should be large, high-studded, and well lighted by several windows extending nearly to the ceiling. The windows should all open both at top and bottom for a quick change of air. Besides this it must have a large ventilator, with a strong draught, and adequate means of heating. An abundant supply of soft water is an absolute necessity in all chemical manipulations. Convenience in obtaining and drawing it off after using must be studied. Equally important is a safe and economical means of heating retorts, flasks, evaporating-dish.es, etc., available for each pupil.

3. The two Laboratories. — It may be well to describe minutely the furnishing and equipment of two small laboratories : the first constructed at trifling expense, but of great practical service ; the second somewhat more elaborate and better equipped, but still within the means of the majority of public and private schools. Both are descriptions of laboratories actually built and successfully used, and the quotations of figures are real ones, from the carefully kept accounts of construction. In both, provisions are made for the individual work of twelve pupils. Of course the dimensions of apartments and the present and prospective requirements of schools will modify these calculations.

LABORATORY No. 1.

We will proceed on the supposition that the building in which this laboratory is to be fitted up is supplied with neither water nor illuminating-gas. These desiderata must be supplied as well as possible.

4. Water Supply. — Obtain a sound, strong molasseshogshead (with iron hoops, if possible). Eemove one head, and set upon a strong platform of planks thirty-six inches high, in a corner of the room, and near a window. Get a tinman to conduct the water from the roof into the hogshead. This can be done through the window, by removing a pane of glass, and inserting in its place a piece of tin, perforated for 'the admission of the tin conductor. From a point three inches below the top of the hogshead carry out through the tin " pane " a waste-pipe of the same size as the conductor. Obtain a piece of gas-pipe as long as the distance from the hogshead to the end of the room. Have iron faucets fitted to the end and middle of this pipe, and by means of it carry water from the hogshead the length of the room at a height of three and one-half feet from the floor. If desirable, turn an iron faucet into the hogshead itself, and water can be drawn in three different parts of the room at once. The waste water can be poured into large earthen crocks provided for the purpose, collected at the close of the exercise and carried out.

5. Heating. — In lieu of Bunsen burners and gas, small glass lamps, burning alcohol, will be used for heating purposes.

6. Laboratory Table.

DIMENSIONS.

FT. IN.

Length 12 6

AYidth 4 4

Height 3

" " shelf a a . . .09

Width of shelf a . . . 6

Height of shelves c c c . .20

FlG.I.

Fig. 1 represents a very convenient table adapted for twelve pupils. Each side is divided into three sections, each section being used by two pupils in common. Such an arrangement has many advantages. With every facility, abundant apparatus and chemicals, there is a great gain in providing for pupils in general chemistry to work in pairs. They are mutually helpful in the at first troublesome manipulations, and the saving in amount of apparatus and quantity of chemicals by such an arrangement is very considerable.

The figure will for the most part explain itself. It should be made of -J pine stock, comparatively "clear." The top should be left unpainted. The remainder can be b b painted, or, better, covered with several coats of hard oil finish, or left in the natural condition, as taste and funds may direct. The shelf a a, and the space upon the table beneath, will be used for bottles and small pieces of apparatus. The partition b b should be carried down through to the floor, dividing the table into lateral halves. The shelves c c c below are for larger pieces of apparatus, and each pupil's private effects. Under the shelf in each section can be placed an earthen crock for the reception of waste water and other matter.

7. Storage Closet. — This should be made of the same well-seasoned stock as the table, with joints close fitting enough to keep out all dust. Convenient dimensions will be 8 feet in length, 7 feet in height, and 1 foot 5 inches deep. A central partition should divide the case into two sections. One side will be fitted up for the storage of chemicals. Leaving ample space in the bottom for the reception of large bottles of acids, let the upper part of the section be provided with shelves made each with three ledges, one above and back of another, like the successive steps in a flight of stairs. These ledges, about three inches in height, will be a great convenience in the arrangement of bottles of different sizes, placing the largest upon the highest ledges.

The other section will receive the glassware and apparatus, and can be made convenient by means of plain, deep shelves at suitable distances from each other.

8. Lecture Table. — There should be sufficient space in the room chosen for a laboratory, or an adjoining one, for the recitations on the subject, and the lecture table should be conveniently placed in this room. Such a table is indispensable for the performance of general class experiments, not profitably to be given to the members of a class, for illustrations in the course of a recitation, and as furnishing a deep tank necessary in the transferring of gases from one vessel to another.

For illustration of such a table see Fig. 3. The table for Laboratory No. 1 is of the same general construction as the one described in Section 14, but may be made of cheaper materials and painted in a less expensive manner. Considerable expense may be saved by building, instead of the drawers, plain lockers, and the convenience of these may be enhanced by putting a horizontal shelf through the middle of each locker.

9. Hood. — A close box or hood, within which all operations involving the generation of poisonous gases can be carried on, should be a part of the equipment of every laboratory. This box should be well lighted, constructed so tight that no gas can escape into the room, and arranged to conduct the gases generated either into a ventilator-box, with an unfailing upward draught, or directly to the open air through a window. In Section 16 is described a very perfect but somewhat expensive hood. An excellent substitute is the following:

Make a box-frame of f pine stock 18 inches deep, of such dimensions as to be set within the frame and fit up closely against the sash of the window least used in the laboratory. Purchase a glazed sash of the size of the inside dimensions of the box-frame and arrange it to slide up and down in one side of the frame like a window. With hooks on the box and screw-eyes in the lower sash of the window, clamp the box closely to the window so that the lower window-sash shall form one side, and the new sliding sash the other side of a tight box. Fit into the top of the box an elbow-joint of small stove-pipe, and pass this pipe out through the upper sash by removing one of the panes of glass and substituting a piece of tin perforated for the passage of the pipe. For ventilation of the box bore several holes in the lower rail of the window-sash, and, to insure an upward draught, a little more than half-way up on one of the wooden sides of the box place a lamp-bracket, and set a lighted kerosene lamp in the bracket whenever the hood is to be used. The cost will be about $2.50.

10. Equipments.

Apparatus and Glassware.

Alcohol lamps. (See section 45.)

Aspirators. (See section 30.)

Bags for gases. (See section 32.)

1 dozen beakers, 2£ ounces, at .15 . . . . $ 1.80

Bell-jars, tubulated. (See section 38.)

Mouth blowpipes. (See section 46.)

Gas-bottles (horseradish bottles, etc., from home).

3 dozen 4-oz. bottles, with ground stoppers, at $ 1.35 4.05

1 dozen one-quart fruit-jars 1.50

Book of chemical labels 50

6 clamps for test-tubes. (See section 36.)

6 earthen crocks 72

10 dozen assorted corks . . . . . . 1.20

Cover glasses. (Cut up pieces of broken windowpanes into squares 4x4 inches.) Se* of cork-borers. (See section 41.)

2 j*und files 40

1 shoekaife for cutting corks .... .35

1 flat file .35

6 Hessian crucibles, 4£-inch .60

6 deflagrating spoons. (See section 42.)

6 porcelain evaporating-dishes, 3-inch .. . .1.50

1 pack of filter-paper, 6-inch .40

4 flasks, flat bottomed, 8-ounce 1.85

12 flasks, flat bottomed, 4-ounce . . . . 1.20 6 glass funnels, 3-inch 90

2 lbs. glass-tubing (assorted numbers) . . . 1.00

2 graduates, 4-ounce 80

6 large nappies (for pneumatic pans) . • . 2.10 Generators for hydrogen, etc. (See section 31.)

CONSTRUCTION AND EQUIPMENT OF LABORATORIES.

3 Wedgewood mortars, 3-inch 2.40

Platinum wire, | pwt .30

foil, |pwt 30

2 potash bulbs (one bulb) .80

1 iron retort 3.00

24 feet rubber-tubing, T 5 g-inch 1 3.60

1 pair of scales, platform 5.00

6 retort stands. (See section 35.)

3 dozen test-tubes, 6-inch 1.08

6 thistle-tubes 72

6 testrtube brushes. (Tie pieces of fine sponge to a

stout wire.)

3 U-tubes, 4-inch 75

Wash-bottles. (See section 43.)

Wire gauze, 1 square foot 50

Lead-pan. (Make it from sheet-lead, as directed for

making sand-bath. See section 39.)

Chemicals.

Alcohol, 2 quarts. (Price variable.) ... $ 1.20

Alum, 8 ounces 05

Aqua ammonia, 1 pound .20

Ammonium chloride, 1 pound 25

Ammonium nitrate, 1 pound . . . . . . .40

Antimony, metal, 4 ounces 10

Arsenious acid, 2 ounces ...... .10

Bone-black, 1 pound 30

Calcium chloride .40

Camphor, £ pound .25

Carbon disulphide, 1 pound 50

Chlorhydric acid, 5 pounds .35

Cochineal, 2 ounces 10

Copper-filings, \ pound .25

" oxide, 1 ounce 20

1 Some tubing of a smaller size may be used for connection.

ELEMENTARY CHEMICAL TECHNICS.

Ether, 1 pint 80

Fluor-spar, 1 pound .15

Iron sulphate, 1 pound 05

Lead acetate, 2 ounces .10

" oxide, 8 ounces 10

Litmus, 1 ounce .15

Magnesium ribbon, 1 pwt 25

Manganese, black oxide, 2 pounds ... .30

Nitric acid, 5 pounds 75

Nut-galls, 2 ounces .10

Oxygen mixture, 3 pounds 1.20

Phosphorus, 1 ounce .25

Potassium, metallic, J ounce 1.00

" bichromate, 1 pound .... .25

" bromide, 4 ounces 40

" iodide, 2 ounces 80

" hydrate, 1 pound .75

" chlorate, 2 pounds 60

" cyanide, 2 ounces .... .10

" ferrocyanide, £ pound 25

" nitrate, 1 pound .20

" permanganate, 1 ounce 20

" tartrate, 2 ounces . . . . .10

Silver nitrate, 1 ounce 90

Sodium, metallic, I ounce .50

acetate, | pound 30

bicarbonate, 1 pound .... .12 hydrate .75

chloride, coarse, 5-pound box . . . .10 " fine, 3 pounds .... .09

nitrate, 1 pound 25

biborate, \ pound .10

silicate, 1 pint 15

Strontium nitrate, 4 ounces 10

Sulphur-roll, 1 pound .06

Sulphur-flowers, 1 pound 10

Sulphuric acid, 10 pounds .25

Turpentine, spirits of, -J- pint 30

Zinc chloride, 1 ounce .25

Zinc, granulated. (See section 58.)

Almost every manufactory of iron, woollen, or cotton goods uses sulphuric acid, where it can be purchased (as an accommodation) at the price quoted. Manufactories of woollen fabrics use chlorhydric and nitric acid. These acids, commercially pure, can often be obtained at such places much cheaper than of dealers in chemicals. Many of the chemicals will keep, unimpaired in quality, for an indefinite period. It is much cheaper to purchase such in bulk, and it is so directed in the above list. Keep all such chemicals in one and two quart fruit-jars. They are cheaper than regular salt-bottles, and, having wide mouths and tight covers, are equally good. Thus preserved the supply of many substances given will be sufficient to last for years.

11. Cost of such a laboratory, fitted up for a class of twelve pupils in general chemistry, is :

Hogshead and water-pipe $ 3.50

Large table 25.00

Lecture table 16.00

Tank 5.30

Storage closet 20.00

Hood 2.50

Apparatus and glassware 39.67

Chemicals 18.40

12. Laboratory No. 2. — This provides for the same number of pupils as the first described, but is fitted up in a

ELEMENTARY CHEMICAL TECHNICS.

Fig. 2.

more complete and expensive manner, for work both in general chemistry and qualitative analysis

It presupposes that the school building is supplied with gas and water, and provides only for bringing both into the room, and carrying the waste-water out

13. Working Table. -Fig. 2 represents the table for the use of the pupils. It is made of white-wood, and stained, or of hard wood, and filled, and is of the same

6 mXH aS g ; V6n - n Kg " L Each P U P° has a d ~> 6 rnch.es deep, for private effects, and a locker, 22 inches

high, for larger pieces of apparatus.

J" *! le ' en <fosed spaces g g g, 1 foot in width, necessarily created by the set bowls, are placed earthen crocks to Z ceive solid matter that might clog the waste-pipes.

The backs of these little recesses should be readily removable in order to give access to the interior of the table in case the plumbing gets out of order.

On each side are three set bowls, nine inches in diameter, without stoppers, each conveniently placed for the use of two pupils. At e c c are gas-cocks furnished with straight tubes for supplying gas to the Bnnsen bnrners by means of f-mch rubber tubine

DIMENSIONS. ft. m.

Length 8

Width 3 10

Height 3

14. Lecture Table. — Fig. 3 represents the lecture table. It is of white-wood, or hard wood stained or filled, and varnished. The top should only be treated to several coats of shellac.

At a is a lead-lined water-tank, 30 x 18 inches in area, and 24 inches deep at one end. The other end should be but 3 inches deep for a distance of 12 inches. By this means bell-jars can be filled with water, inverted, and stand in shallow water. This is a much better arrangement than soldering cleats upon the sides of the tank and putting in slate shelves. Such shelves are pretty sure to break down at an unfortunate time.

The table is supplied with water-cock, waste-pipe from the tank, and two gas-cocks for supplying fuel to two Bunsen burners.

15. Storage Closet. — The plan is the same as described in section 7, but the closet is built of better stock, ornamented with a cornice at the top, painted, has four glass

ELEMENTARY CHEMICAL TECHNICS.

Height

DIMENSIONS.

FT. IN. FT. IN

FIG. 4.

doors instead of wooden ones, as in the cheaper closet, and is of larger dimensions, being 11 feet in length, 7 feet in height, and 1 foot 5 inches deep.

16. Hood. — Fig. 4 represents a convenient hood. It consists of a chamber with bottom and two sides of wood. The remaining sides are window-sashes with four 11 x 11 inch lights. One of the sashes is made to slide up and down as in an ordinary window. A dome-like roof of zinc is securely fitted upon the top of the chamber. The four sloping sides of this roof are narrowed until they reach a six-inch collar, over which is slipped a length of funnel which passes into a ventilator-box. The chamber is fastened, by means of large brackets, to the side of the room at a convenient height. Inside the chamber, upon one of the wooden sides, screw up a lamp-bracket to hold a large kerosene lamp. This should be kept constantly burning, while the hood is in use, to assure an ascending current. Remember that an upward draught cannot be secured without a corresponding inlet for cold air, and raise the sash a very little. If a ventilator-box is not available, carry the pipe of the hood out through a window, as directed in section 9.

17. Plumbing. — The water-pipes should be so placed that every foot of them can be easily reached. Let the discharge pipes from the bowls be carried into a drain-tile main, and the latter must be securely trapped. Provide for shutting off the water supply and draining the pipes in cold weather.

18. Equipments.

Apparatus and Glassware.

Beakers, 2 dozen 2|--ounce $ 3.60

8 Bunsen burners, with ring 4.00

6 mouth blowpipes . . . . . . 1.50

1 hot-blast blowpipe, for working glass . . . 3.00

1 book chemical tables .50

6 dozen glass bottles, 4-ounce, ground stoppers . 8.10

1 nest Hessian crucibles .30

6 earthen crocks 72

1 set of brass cork-borers 2.50

6 test-tube brushes 72

10 dozen corks, assorted sizes .... 1.20 Cover glasses. (See preceding list of apparatus.)

6 deflagrating spoons 1.20

6 evaporating dishes, 3-inch 1.50

1 pack of filter-paper, 6-inch .40

3 files, round, fiat, three-cornered 60

2 dozen 4-ounce flasks 2.40

ELEMENTARY CHEMICAL TECHNICS.

4 dozen 8-ounce flasks 85

6 funnels, 3-inch 90

2 pounds glass-tubing (assorted numbers) . . 1.00

6 generators. (See section 31.)

1 graduate, 4-ounce 40

1 " English and Metric 90

2 gas-bags, 55 gallons 25.00

1 dozen gas-jars (use fruit-jars) .... 1.50

1 dozen litmus-papers 40

6 Wedgewood mortars, 3-inch .... 2.40 6 nappies (large for pneumatic pans) . . . 2.10

40 feet rubber-tubing, ^ 6.00

Chemical scales 12.00

6 iron retort-stands, 3 rings 5.00

1 iron retort for making oxygen .... 3.00 1 chemical thermometer . . . . . 2.25 6 dozen test-tubes, 6-inch 2.16

3 dozen " " 4-inch ..... 1.20 Test-tube holders. (See section 36.)

6 thistle-tubes .72

3 U-tubes, 4-inch 75

3 chloride of calcium tubes .90

Tube for hydrogen tone 50

Wash-bottles. (See section 43.)

Brass wire gauze .50

Iron " " (use mosquito-netting).

Chemicals.

Alcohol, 1 quart

Arsenious acid, 2 ounces ....

Alum, £ pound . ...

Ammonia, 5-pint bottle ....

Ammonium carbonate, 1 pound

" chloride, " " . .

nitrate, crystals, 1 pound .

Aniline, red, | ounce

Antimony (metallic), \ pound

tartrate (Tartar emetic), 1 ounce Amount carried forward

Barium hydrate, 1 ounce 25

Barium sulphate, 1 " .10

Benzole, 1 pint 30

Bone-black, 1 pound .30

Borax, 1 pound .20

Bromine, 1 ounce .25

Calcium chloride, 1 pound 40

fluoride, 1 " 15

" sulphate, 1 " 10

Camphor, £ pound .25

Carbolic acid, 1 ounce 15

Carbon disulphide, 1 pound .50

Cochineal, 2 ounces 10

Copper trimmings, 1 pound .50

" wire gauze 40

Copper oxide, 1 ounce .20

" sulphate, 2 pounds .24

Chlorhydric acid, 5 pounds .35

Ether, sulphuric, 1 pint 80

Nut-galls, 1 ounce .05

Gun-cotton, ± ounce 15

Iodine, 1 ounce .50

Iron sulphate, 1 pound 05

Lead acetate, 2 ounces .10

" nitrate, 2 ounces .10

" oxide, | pound 10

Lithium carbonate, £ ounce .25

Litmus, 1 ounce 10

Magnesium, 1 pwt. (ribbon) .25

Manganese, black oxide, 3 pounds ... .45

Mercury, 2 pounds 1.50

" red oxide, 2 ounces .30

Nitric acid, 5 pounds 75

Nickel sulphate and ammonia, 2 ounces . . .40

Oxygen mixture, 5 pounds 2.00

Phosphorus, 1 ounce .25

ELEMENTARY CHEMICAL TECHNICS.

Platinum foil, 1 pwt 60

Platinum wire, 1 pwt .60

Potassium, £ ounce 1.00

" bromide, 2 ounces . . . . .20

" bicarbonate, 1 pound 40

" bichromate, 2 pounds .... .50

" hydrate, 1 pound .75

" chlorate, 3 pounds 90

" cyanide, ± pound .20

" ferrocyanide, £ pound 25

" iodide, 1 ounce .40

" nitrate, 1 pound 20

Potassium permanganate, 1 ounce ... .20

Silver nitrate, 1 ounce 90

Sodium, metallic, i ounce .50

" acetate, £ pound 30

" bicarbonate, 1 pound .12

" hydrate, 1 pound .75

" chloride, 5-pound box 10

" " (coarse fine) 3 pounds . . .09

" nitrate, 1 pound 25

" silicate, 1 pint .15

Strontium nitrate, | pound .20

Sulphur-roll, 1 pound 06

" flowers, 1 pound .10

Sulphuric acid, 10 pounds 25

Tinfoil (pure), \ pound .35

Turpentine, 1 pint 60

Zinc, chloride, 1 ounce .25

Zinc, granulated, 4 pounds 1.20

19. Cost of Laboratory No. 2.

Plumbing 45.00

Laboratory table 40.00

Lecture 23.00

Tank 5.30

Storage closet 45.00

Painting 20.00

Apparatus and glassware 102.67

The list of chemicals is a general one, selected with a view to the use of no particular text-book. Of course the list can be modified to adapt it to any series of experiments a teacher may choose to have demonstrated. The prices of apparatus and chemicals quoted are many of them list prices. If purchases are made in considerable quantities, as is always advisable, from 10 to 15 per cent may be deducted in the estimates of the amount of the last two items.

20. Labelling Chemicals. — All bottles and packages of chemicals should be labelled before they are placed in the storage closet. Books of printed labels, with structural formulas of the substance named, can be purchased, and are exceedingly convenient. In lieu of these, gummed labels 1\ x 1 inch may be purchased in small boxes. The names should be written accurately in ink.

CHAPTEE II.

GLASS- WORKING.

21. A Supply of Soft Glass Tubing should be purchased by the pound and kept constantly on hand.

Fig. 5.

The sizes should run from one to eight. Sizes 3 and 4 will be used more than others. Eubber tubing of the same calibre can be readily obtained, and tight but easily adjusted joints thus made. A small quantity of hard glass tubing, of sizes 2, 3, and 4, will also be required. Small tubing can be broken squarely at any point by scratching the glass at that point with a three-cornered file, and applying pressure against the opposite side of the tube from the scratch. The sharp broken edges should be removed by softening the end in the gas-flame or by grinding the ends of the tube in the manner described in Section 23.

22. Boring Glass. — Holes large or small can be bored through the hardest glass, without any danger of cracking or shivering the glass, as follows :

Dissolve gum-camphor in spirits of turpentine until a nearly saturated solution is obtained. Provide a number

GLASS- WORKING. 19

of round files (new) of different sizes. Break off the tip of each file so as to riiake a sharp, ragged end. Select the smallest file. Dip the end in the turpentine solution, and, holding the file at an angle of about 45° with the surface of the glass, at the same time press the ragged tip against the glass and move the file rapidly to and fro. A depression will immediately be made in the glass, and its thickness soon cut through. The teeth of the file can then be used. Keep the files constantly wet with the solution. Enlarge the orifice with files of successive sizes. Use files but a little smaller than the orifice itself.

23. Grinding Glass. — Large surfaces of glass can be cut away and ground very rapidly, and without any danger of breaking, by using flat files constantly wet in the turpentine solution." If accurate grinding of plane surfaces is required, another device is necessary. Bell-jars may be made to fit the pump-plate, or pneumatic jars squared off for use with cover-glasses, on a lathe. Prepare a disk of hard wood 1£ inches in thickness, and with a diameter con^ siderably larger than that of the largest jar to be ground. ]\felt together pitch, tallow, and glue in the proportion of 10 parts of the first, 2 of the second, and 5 of the last, and stir into the fluid just before it cools (not too soon, or it will settle irregularly through the mass) a large quantity of medium fine emery. Coat the face of the disk thickly with this mixture while it is hot enough to spread easily. In a few hours the disk will have a good grinding surface. Attach this improvised emery-wheel to the shaft of the lathe, or even upon a common whirling-table. Keep the surface wet with the turpentine solution. Hold the jar firmly and squarely against the revolving disk.

24. Cutting Glass. — Plane surfaces of glass can be cut in straight lines or curves ; large tubing, necks and bottoms of bottles cut off very easily and rapidly by taking ad vantage of the expansion of glass when heated. The disks of hardened steel made for cutting glass often work well for a short time, but are liable to give out suddenly. Good diamonds are expensive, easily broken, will cut well only in straight lines, and always leave a sharp cutting-edge. None of the objections are to be met with in using heat. The tools are very simple and inexpensive. Procure two rods of soft iron (not steel) from § to % inch in diameter, one 12, the other 15 inches in length. The best possible material is the soft iron rod, used to fasten together the parts of a stove, obtainable at any stove store. The shorter one should be perfectly straight. Bend the longer one in a somewhat sharp compound curve. Insert them in wooden handles which can be purchased at a hardware store. To cut a plane surface, as a window-pane, heat the straight rod, if the glass is quite thick (J inch or more), to a red heat; if thinner, not so hot. Then with a three-cornered file, wet with the turpentine solution, cut a deep groove in the edge of the glass and place the glass upon the even surface of a table. Place the heated rod flat upon the glass, with the end ^ f an inch below the filemark. Now draw the rod downward in the direction in which you wish the cut to run, and the crack will follow if you keep the rod about £ of an inch ahead of it. If the rod is very hot, be careful that the crack does not quite catch up. If it does, it may dart on and take a direction of its own. With a camel's-hair brush dipped in black paint, or with pen and ink, mark out any design in circles or scallops, curves or straight lines. A little practice will enable one to cut the glass by these lines with perfect accuracy, and the edges will be much smoother than when cut with a diamond.

25. To cut open Large Tubing, bottles, etc., heat the curved rod. With the file, wet as before, cut a groove from

GLASS-WORKING. 21

\ to £ inch in length, according to the size of the tubing or bottle, and nearly through the thickness of the glass. Wipe off the turpentine solution from the vicinity of the groove. Place the heated rod first against the end of the groove in the position a in the figure, and wait until the glass is heard to crack. Then press it against the other end of the groove in the position b, and the crack will start and follow the rod round the bottle in the direction indicated by the arrow.

26. To bend Tubing. — To bend large tubing pack it full of fine sand, and heat it in a charcoal or bituminous-coal fire. Get a blacksmith to accommodate you with his forge fire.