Gas and fuel analysis for engineers

Front matter

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K UH nun

■I

Preface

This little book is an attempt to present in a concise yet clear form the methods of gas and fuel analysis involved in testing the efficiency of a boiler plant. Its substance was given originally, in the form of lectures and heliotyped notes, to the students in the courses of Chemical, Mechanical, and Electrical Engineering, but in response to requests it has been deemed expedient to give it a wider circulation.

At the time of its conception, nothing of the kind was known to exist in the English language ; in German we now have the excellent little book of Dr. Ferdinand Fischer, " Taschenbuch fur Feuerungs- Techniker."

The present book is the result of six years' experience in the instruction of classes of about one hundred students. It is in no sense a copy of any other work, nor is it a mere compilation. The author has in every case endeavored to give credit where anything has been taken from outside sources; it is, how-

IV PREFACE.

ever, difficult to credit single ideas, and if he has been remiss in this respect it has been unintentional.

The study of flue-gas analysis enables the engineer to investigate the various sources of loss ; and if this compend stimulates and renders easy such investigation, the writer's purpose will have been accomplished. The necessary apparatus can be obtained from the leading dealers in New York City.

The author wishes to acknowledge his indebtedness to our former Professor of Analytical Chemistry, Dr. Thomas M. Drown, and to Mrs. Ellen H. Richards, by whose efforts the department of Gas Analysis was established.

He will also be grateful for any suggestions or corrections from the profession.

Massachusetts Institute of Technology, Boston, November, 1896.

Preface To The Sixth Edition

The changes made in the present edition consist in the addition of Specifications for the Purchase of Coal and Fuel Oil and of the Sampling of Fuel Oil and Natural Gas.

As in the past, minor additions and corrections nave been made where necessary to bring the book up to present practice.

Massachusetts Institute of Technology, Boston, November, 191 1.

Appendix

Tables 109

LIST OF ILLUSTRATIONS.

i. Gas Sampling-tube 3

2. Sampling Apparatus 4

3. Sampling Apparatus for Mine-gases 5

4. Gas-tube 5

5. Richards's Jet-pump 8

6. Bunsen's Pump 8

7. Steam Air-pump 9

8. Orsat Gas Apparatus 12

9. Bunte Gas Apparatus 17

10. Elliott Gas Apparatus 21

11. Melting-point Boxes 27

12. Hemfel Gas Apparatus 37

13. Hempel Gas Apparatus 38

14. Muencke's Aspirator 56

15. Combustion-furnace 74

16. Mahler Bomb 83

17. Mahler Bomb and Calorimeter 84

18. Parr's Calorimeter 93

19. Junkers' Gas-calorimeter, Section 99

20. Junkers' Gas-calorimeter 100

vii

GAS AND FUEL ANALYSIS.

Chapter I. Introduction And Methods Of Sampling

Until within recent years, the mechanical engineer in testing a boiler plant has been compelled to content himself with the bare statement of its efficiency, little or no idea being obtained as to the apportionment of the losses. Knowing the composition and temperature of the chimney-gases and the analysis of the coal and ash, the loss due to the formation of carbonic oxide, to the imperfect combustion of the coal, to the high temperature of the escaping gases, can each be determined and thus a basis for their reduction to a minimum established.

By the simple analysis of the chimney-gases and determination of their temperature, a very good idea of the efficiency of the plant can be obtained previous to making the engineering test. For example, in a test which the author made in connection with his students, the efficiency was increased from 58 to 70 per cent, upon the results of the gas analysis alone.

To this end a representative sample must be collected according to the method about to be described.

SAMPLING.

Before proceeding to take a sample of the gas, the plant — for example, a boiler setting — from which the gas is to be taken should be thoroughly inspected, and all apertures by which the air can enter, carefully stopped up. A suitable tube is then inserted air-tight in the gas-duct, connected with the sampling or gas apparatus, and suction applied, thus drawing the gas out. Cork, putty, plaster of Paris, wet cotton-waste, or asbestos may be used to render the joint gas-tight. The place of insertion should be chosen where the gas will be most completely mixed and least contaminated with air. The oil-bath containing the thermometer is similarly inserted near the gas-tube, and the temperature read from time to time.

I. Tubes. — The tubes usually employed are Bohemian-glass combustion tubing or water-cooled metal tubes; those of porcelain or platinum are also sometimes used. Glass and porcelain tubes when subjected to high temperatures must be previously warmed or gradually inserted: the former may be used up to temperatures of 6oo° C. (1200 F.). Uncooled metal tubes, other than those of platinum, should under no circumstances be used.*

* Fischer, " Technologie der Brennstoffe," 1880, p. 221, states that the composition of a gaseous mixture was changed from 1.5 to 26.0 per cent carbon dioxide, by the passage through an iron tube heated to a dull red heat, the carbonic oxide originally present reducing the iron oxide with the formation of carbon dioxide.

INTRODUCTION AND METHODS OF SAMPLING. 3

The metal tube with the water cooling is made as shown in Fig. I, c being a piece of brass pipe 3 feet long, \\ inches outside diameter, b the same length, J inch in diameter, and a \ inch in diameter. The water enters at d and leaves at e. The walls of

Fig. 1. — Gas-sampling Tube.

the tubes are T \ inch thick. The joint at A should be brazed; the others may be soldered.

Platinum tubes from their high cost and small bore are seldom used; they are attacked by carbon, cyanogen, arsenic, and metallic vapors.

2. Apparatus for the Collection of Samples.— A convenient sampling apparatus is shown in Fig. 2. It may be made from a liter separatory funnel— instead of the bulb there shown — fitted with a rubber stopper carrying a tube passing to the bottom and a T tube; both of these, except where sulphur-containing gases are present, can advantageously be made of T Vinch lead pipe. The stopper should not be fastened down with wire between the tubes after the manner of wiring effervescent drinks, as this draws the rubber away from the tubes and occasions a leak. The fastening shown consists of a brass plate fitting upon the top of the stopper, provided with screws and nuts which pass through a wire around

GAS AND FUEL ANALYSIS.

the neck of the separately. A chain fastened to the plate serves as a convenient method of handling it.

In using the apparatus, the bulb is filled with water by connecting the stem with the water-supply and opening one of the pinchcocks upon the T tube; the

Fig. 2.— Sampling Apparatus.

water thus entering from the bottom forces the air out before it. One branch of the T is connected with the sampling-tube and the other with the suctionpump, the stopcocks being open, and a current of gas drawn down into the pump; upon opening the cock upon the stem, the water runs out, drawing a small portion of the gas-current passing through the T after it into the bulb. It is then taken to a convenient

INTRODUCTION AND METHODS OF SAMPLING.

place for analysis, the tube h connected with a head of water, a branch of the T i, with the gas apparatus, and a sample of gas forced over into the letter for analysis.

Fig. 4. — Gas-tube.

Fig. 3. — Sampling Apparatus for Mine-gases.

Enough water should be left in the bulb to seal the stopcock on the bottom and prevent leakage. This apparatus is better adapted for the needs of the classroom than for actual practice, as it enables the same sample to be given to eight or ten students. As has been shown by several years' experience, the water exercises no appreciable solvent action upon the gaseous mixture in the time — about half an hour — necessary to collect and distribute the samples. It is often necessary to attach about a yard of J-inch rubber tubing to the stem of the bulb to prevent air being sucked up through it when taking a sample.

In the actual boiler-test it is preferable to insert a T instead of this apparatus in the gas-stream, connect the gas apparatus to the free branch of this T, and draw the sample. In making connections with gas apparatus the air in the rubber connectors should be displaced with water by means of a medicinedropper.

In the Saxon coal-mines, zinc cans of ten liters capacity, of the form shown in Fig. 3, are used by Winkler for sampling the mine-gases; they are carried down filled with water and this allowed to run out, and the gas thus obtained brought into the laboratory and analyzed. Small samples of gas may very well be taken in tubes of 100 cc. capacity like Fig. 4, the ends of which are closed with rubber connectors and glass plugs. Rubber bags are not to be recommended for the collection and storage of gas for analysis, as they permit of the diffusion of gases, notably hydrogen.

3. Apparatus for Producing Suction. — I. Water-pumps — (a) Jet- pumps, depending for their action upon a considerable head of water, and (J?) those depending rather upon a sufficient fall of water.

INTRODUCTION AND METHODS OF SAMPLING. 7

id) Jet -pumps. — The Richards' jet pump * is shown in section in Fig. 5 and much resembles a boiler injector; it consists of a water-jet w, a constriction or waist a, a waste-tube 0, and a tube for the inspiration of air. The jet of water forms successive pistons across a, drawing the air in with it and is broken up into foam by the zigzag tube o.

This pump is known in Germany as Muencke's, and in England as Wing's; Chapman's pump is also a modified form.

It may be easily constructed in glass, the jets passing through rubber stoppers which are wired down, thus admitting of adjustment to the conditions under which it has to work.f

(b) Fall-pumps. — Bunsen's pump, Fig. 6, consists of a wide glass tube A, drawn out at the bottom for connection with a ^-inch lead pipe b, and at the top for connection with c, the tube through which the air is drawn; this tube is usually fused in, although it may be connected with rubber; a is a rubber tube provided with screw cocks connected with the water-supply; d is connected with a mercury column, and the vessel B serves for the retention of any water which might be drawn back into the apparatus evacuated.

The tube b for the best results should be 32 feet in length, equal to the height of a column of water supported by the atmosphere, although for the ordinary purposes of gas-sampling it may be shorter.

When water is admitted through a it fills fr, acting

* Richards, Am. Jour, of Science (3), 8, 412; Trans. Am. Inst. Min. Engrs., 6, 492 (1874).

f The pump -vill also work well using steam.

GAS AND FUEL ANALYSIS.

as a continually falling piston drawing the current of air through e and its connections. These various forms of water-pumps should give a vacuum repre-

Fig. 5. — Richards' Jet-pump. Fig. 6. — Bunsen's Pump.

sented by the height of the barometer less the tension of aqueous vapor at the temperature at which they are used, or about 29 inches of mercury.

INTRODUCTION AND METHODS OF SAMPLING. 9

II. STEAM-PUMPS.— Kochinke describes the apparatus in use in the Muldner Hutten in Freiberg-, shown at one-fifth size in Fig. 7. It consists of a glass tube drawn down to an opening 6 mm. in diam-

Fig. 7. — Steam Air-pump.

eter; concentric with this, and held in place by the washer a, is the steam-jet 2 mm. in diameter, passing through the cork b y the cement c, and covering d. It is connected with the steam-pipe at g by webbed rubber tubing/"; the air enters at e. This is said to give very good results and be economical in use of steam.

In case . neither water nor steam be available, recourse must be had to the ordinary rubber syringebulbs, provided with suitable valves, obtainable at any rubber store, or to a bottle aspirator. This consists of two one-gallon bottles, provided with doubly perforated rubber stoppers, carrying tubes of glass or lead bent at right angles. In each bottle one of these tubes passes nearly to the bottom, and these are connected together by a piece of rubber tubing a yard long, carrying a screw pinchcock. The other tube in each case stops immediately under the stopper. Upon filling one of the bottles with water, inserting the stopper and blowing strongly through the short tube, water will fill the long tubes thus forming a siphon,

IO GAS AND FUEL .ANALYSIS.

and upon lowering the empty bottle, a current of air will be sucked in through the short tube originally blown into ; this may be regulated by the screw pinchcock.

In inserting the gas-sampling tube care should be taken not to insert it so close to the source of heat as to draw out the gases in a dissociated, i.e. partly decomposed, condition.

In case of very smoky fuels it is well to filter the gases through rolls of fine wire gauze or asbestos ; in sucking them through a washing-bottle, the water may change the composition of the sample.

Chapter II. Apparatus For The Analysis Of Chimney- Gases

In the writer's opinion the apparatus which is best adapted for this purpose is that of Orsat; it is readily portable, not liable to be broken, easy to manipulate, sufficiently accurate, and — in the modification about to be described — always ready for use, there being no stopcocks to stick fast.

As the Bunte and Elliott apparatus are also used for this purpose, they too will be described.

Fischer's apparatus, using mercury, is rather too difficult for the average engineer; HempePs or Morehead's* apparatus for the analysis of illuminating-gas might also be used; it is, however, not customary.

ORSAT APPARATUS.

Description. — The apparatus Fig. 8, is enclosed in a case to permit of transportation from place to place; furthermore, the measuring-tube is jacketed with water to prevent changes of temperature affecting the gas-volume. The apparatus consists essentially of the levelling-bottle A, the burette B, the pipettes P f , P", P'", and the connecting tube T.

* No. 143 Lake Street, Chicago.

II Gas And Fuel Analysis

Manipulation. — The reagents in the pipettes should be adjusted in the capillary tubes to a point on the stem about midway between the top of the pipette and the rubber connector. This is effected by opening wide the pinchcock upon the connector, the affiTrtilB Y.M it

Fig. 8.— Orsat's Gas Apparatus.

bottle being on the table, and very gradually lowering the bottle until the reagent is brought to the point above indicated. Six inches of the tubing used correspond to but o.i cc, so that an error of half an inch in adjustment of the reagent is without influence upon the accuracy of the result. The reagents having been thus adjusted, the burette and connecting tube are completely filled with water by opening d and raising the levelling-bottle. The apparatus is now ready to receive a sample of gas (or air for practice). In case a flue-gas is to be analyzed d is connected with t, Fig. 2, A lowered and about 102 cc. of the gas forced over by opening h\ or d may be connected with aT joint in the gas-stream; the burette after filling is allowed to drain one minute by the sand-glass, c snapped upon its rubber tube, and the bottle A raised to the top of the apparatus. By gradually opening c the water is allowed to run into the burette until the lower meniscus stands upon the 100 or o mark (according to the graduation of the apparatus). The gas taken is thus compressed into the space occupied by 100 cc, and by opening d the excess escapes. Open c and bring the level of the water in the bottle to the same level as the water in the burette and take the reading, which should be 100 cc. Special attention is called to this method of reading: if the bottle be raised, the gas is compressed; if lowered, it is expanded.

Determination of Carbon Dioxide. — The gas to be analyzed is invariably passed first into pipette P', containing potassium hydrate for the absorption of carbon dioxide, by opening e and raising A. The gas displaces the reagent in the front part of the pipette, laying bare the tubes contained in it, which being covered with the reagent present a large absorptive surface to the gas; the reagent moves into the rear arm of the pipette, displacing the air over it into the flexible rubber bag which prevents its diffusion into the air. The gas is forced in and out of the pipette by raising and lowering^, the reagent finally brought approximately to its initial point on the stem of the pipette, the burette allowed to drain one minute, and the reading taken. The difference between this and the initial reading represents the cubic centimeters of carbon dioxide present in the gas. To be certain that all the carbon dioxide is removed, the gas should be passed a second time into P' and the reading taken as before; these readings should agree within o. I per cent.

Determination of Oxygen. — The residue from the absorption of carbon dioxide is passed into the second pipette, P" , containing an alkaline solution of potassium pyrogallate, until no further absorption will take place. The difference between the reading obtained and that after the absorption of carbon dioxide, represents the number of cubic centimeters of oxygen present.

Determination of Carbonic Oxide. — The residue from the absorption of oxygen is passed into the third pipette, P ! " , containing cuprous chloride, until no further absorption takes place; that is, in this case until readings agreeing exactly (not merely to o. i) are obtained. The difference between the reading thus obtained and that after the absorption of oxygen, represents the number of cubic centimeters of carbonic oxide present.

Determination of Hydrocarbons. — The residue left after all absorptions have been made may consist, in addition to nitrogen, the principal constituent, of hydrocarbons and hydrogen. Their determination is difficult for the inexperienced, and, if desired, a sample of the flue-gas should be taken, leaving as little water in the apparatus as possible, and sent to a competent chemist for analysis.

Accuracy. — The apparatus gives results accurate to 0.2 of one per cent.

Time Required. — About twenty minutes are required for an analysis ; two may be made in twenty-five minutes, using two apparatus.

Notes. — The method of adjusting the reagents is the only one which has been found satisfactory: if the bottle be placed at a lower level and an attempt made to shut the pinchcock c upon the connector at the proper time, it will almost invariably result in failure.

The process of obtaining ioo cc. of gas is exactly analagous to filling a measure heaping full of grain and striking off the excess with a straight-edge; it saves arithmetical work, as cubic centimeters read off represent percent directly.

It often happens when e is opened, c being closed, that the reagent in P' drops, due not to a leak as is usually supposed, but to the weight of the column of the reagent expanding the gas.

The object of the rubber bags is to prevent the access of air to the reagents, those in P" and P" f absorbing oxygen with great avidity, and hence if freely exposed to the air would soon become useless.

Carbon dioxide is always the first gas to be removed from a gaseous mixture. In the case of air the percentage present is so small, 0.08 to o. 1, as scarcely to be seen with this apparatus. It is important to use the reagents in the order given ; if by mistake the gas be passed into the second pipette, it will absorb not only oxygen, for which it is intended, but also carbon dioxide; similarly if the gas be passed into the third pipette, it will absorb not only carbonic oxide, but also oxygen as well.

The use of pinchcocks and rubber tubes, original with the author, although recommended by Naef,* is considered by Fischer, f to be inaccurate. The experience of the author, however, does not support this assertion, as they have been found to be fully as accurate as glass stopcocks, and very much less troublesome and expensive.

In case any potassium hydrate or pyrogallate be sucked over into the tube T or water in A, the analysis is not spoiled, but may be proceeded with by connecting on water at d, opening this cock, and allowing the water to wash the tubes out thoroughly. The addition of a little hydrochloric acid to the water in the bottle A will neutralize the hydrate or pyrogallate, and the washing may be postponed until convenient.

After each analysis the number of cubic centimeters of oxygen and carbonic oxide should be set down upon the ground-glass slip provided for the purpose. By adding these numbers and subtracting their sum from the absorption capacity (see Reagents) of each reagent, the condition of the apparatus is known at any time, and the reagent can be renewed in season to prevent incorrect analyses.

BUNTE APPARATUS.

Description. — The apparatus Fig. 9 consists of a burette — bulbed to avoid extreme length — provided

* Wagner's Jahresb. 1885, p. 423.

f Technologie d. Brennstoffe, foot note p. 295.

ANALYSIS OF CHIMNEY-GASES.

i;

at the top with a funnel F and three-way cock/, and a cock / at the bottom. These stopcocks are best of the Greiner and Friedrichs obliquely bored form. The burette is supported upon a retortstand with a spring clamp.

A "suction-bottle " S, an 8-oz. widemouthed bottle, fitted similarly to a wash-bottle, except that the deliverytube is straight and is fitted with a four-inch piece of J-inch black rubber tubing, serves to withdraw the reagents and water when necessary, A reservoir to contain water at the temperature of the room, fitted with along rubber tube, should be provided for washing out the reagents and filling the burette.

Manipulation. — Before using the apparatus, the keys of the stopcocks should be taken out, wiped dry, together with their seats, and sparingly smeared with vaseline or a mixture of vaseline and tallow and replaced. The Fig. 9.— Bunte's completeness of the lubrication can be Gas Apparatus - judged by the transparency of the joint, a thoroughly lubricated joint showing no ground glass. The burette is filled with water by attaching the rubber tube to the tip at / and opening the stopcocks at the top and bottom ; j is connected with the source whence the gas is to be taken, turned to communicate with the burette and opened, about 102 cc. of gas allowed to run in, and /and /closed.

The cup F is filled with water to the 25-cc. mark, j turned to establish communication between it and the burette, the burette allowed to drain one minute by the sand-glass, and the reading taken, the cup being refilled to the mark if necessary. The readings are thus taken under the same pressure each time, i.e., this column of water plus the height of the barometer; and as the latter is practically constant during the analysis, no correction need be applied, it being within the limits of error.

Determination of Carbon Dioxide. — The "suction-bottle " is connected with the tip of the burette, / opened, and the water carefully sucked out nearly to /. The bottle is now disconnected, the burette dismounted from its clamp, using the cup as a handle, and the 25 cc. of water turned out. The tip is immersed under potassium hydrate contained in the No. 3 porcelain dish, and the cock / opened, then closed, and the tip wiped clean with a piece of cloth. The burette is now shaken, holding it by the tip and the cup, the thumbs resting upon j and /; more reagent is introduced, the absorption of the gas causing a diminished pressure, and the operation repeated until no change takes place. The cup is now filled with water, j opened, and the leagent completely washed out into an ordinary tumbler placed beneath the burette. Four times filling of F should be sufficient for this purpose. The cup is now filled to the 25-cc. mark, j opened, and the reading taken as before.

The difference between this reading and the initial represents the number of cubic centimeters of carbon dioxide; this divided by the volume of the gas taken gives the per cent of this constituent.

Determination of Oxygen. — The water is again sucked out, and potassium pyrogallate solution introduced, similarly to potassium hydrate; this is displaced by water, and the reading taken as before. The difference between this and the last reading is the volume of oxygen present.

Determination of Carbonic Oxide. — The water is removed for a third time, and acid cuprous chloride solution introduced and the absorption made as before; this is washed out, first with water containing a little hydrochloric acid to dissolve the white cuprous chloride which is precipitated by the addition of water, and finally with pure water, and the reading taken as before. The difference between this and the preceding gives the volume of carbonic oxide present.

Notes. — Especial care should be taken not to grasp the burette by the bulb, as this warms the gas and renders the readings inaccurate. The stopcocks can conveniently be kept in the burette by elastic bands of suitable size. When the apparatus is put away for any considerable time, a piece of paper should be inserted between the key and socket of each stopcock to prevent the former from sticking fast. To ascertain when the absorption is complete, the burette is mounted in its clamp and allowed to drain until the meniscus is stationary, the dish containing the reagent raised until the tip is covered, /opened, and any change in level noted. If the meniscus rises, the absorption is incomplete and must be continued; if it remains stationary or falls, the absorption may be regarded as finished. In case the grease from the stopcocks becomes troublesome inside the burette, it may be removed by dissolving it in chloroform and washing out with alcohol and then with water. The object in sucking the water not quite down to /, thus leaving a little water in the burette, is to discover if / leaks, the air rushing in causes bubbles.

The object in washing out each reagent and taking all readings over water is to obviate corrections for the tension of aqueous vapor over potassium hydrate, hydrochloric acid, or any of the reagents which might be employed. The tension of aqueous vapor over seven per cent caustic soda is less than over water.

Accuracy and Time Required. — The apparatus is rather difficult to manipulate, but fairly rapid — about twenty-five minutes being required for an analysis — and accurate to one tenth of one per cento

ELLIOTT APPARATUS.

Description. — The apparatus Fig. 10 consists of a burette holding ioo cc. graduated in tenths of a cubic centimeter and bulbed like the Bunte apparatus — the bulb holding about 30 cc. ; it is connected with a levelling-bottle similar to the Orsat apparatus. The top of the burette ends in a capillary stopcock, the stem of which is ground square to admit of close connection with the "laboratory vessel," an ungraduated tube similar to the burette, except of 125 cc. capacity. The top of this "vessel " is also closed with a capillary stopcock, carrying by a ground-glass joint a thistle-tube F, for the introduction of the reagents. The lower end of this " vessel " is closed by a rubber

ANALYSIS OF CHIMNEY-GASES.

=w

Sy stopper carrying a three-way cock o, and connected with a levelling-bottle D. The burette and vessel are held upon a block of wood — supported by a ring stand — by fine copper wire tightened by violin keys.

Manipulation. — The ground-glass joints are lubricated as in the Bunte apparatus. The levelling-bottles are filled with water, the stopcocks opened, and the bottles raised until the water flows through the stopcocks m and n. m is connected with the source whence the gas to be analyzed is to be taken, n closed, D lowered and rather more than ioo cc. drawn in, and m closed. 11 is opened, D raised and E lowered, nearly 100 cc. of gas introduced, and 11 closed ; by opening m and raising D the remainder of the gas is allowed to escape, the tubes being filled with water and 111 closed, n is opened and the water brought to the reference-mark; the burette is allowed to drain one minute, the level of the water in E is brought to the same level as in the burette, and the reading taken.

Determination of Carbon Dioxide. — By raising E> opening «, and lowering D, the gas is passed over into the laboratory vessel; F is filled within half an inch

Fig. 10. — Elliott Gas Apparatus.

of the top with potassium hydrate, o closed, m opened, and the reagent allowed to slowly trickle in. A No. 3 evaporating-dish is placed under <?, and this turned to allow the liquid in the laboratory vessel to run into the dish. At first this is mainly water, and may be thrown away; later it becomes diluted reagent and may be returned to the thistle-tube. When the depth of the reagent in the thistle-tube has lowered to half an inch, it should be refilled either with fresh or the diluted reagent and allowed to run in until the absorption is judged to be complete, and the gas passed back into the burette for measurement. To this end close and then in, raise E, open n, and force some pure water into the laboratory vessel, thus rinsing out the capillary tube. Now raise D and lower E, shutting 11 when the liquid has arrived at the reference-mark. The burette is allowed to drain a minute, the level of the water in the bottle E brought to the same level as the water in the burette, and the reading taken.