sive. two perforations, occupied respectively by a thermomefirst instance, are shown in Fig. 1, letters A to F incluA indicates an inch-thick soft-rubber cork, with

TRAIN FOR THE ANALYSIS OF CRUDE GAS, FROM THE HYDRAULIC MAIN OF A GAS WORKS, ETC.

[NOTE.-Between G and H an additional tube, precisely similar to G, charged with chloride of calcium, is employed, which, for simplification has been omitted from the figure.]

ter and an eduction-tube bent at a right angle, inserted into an aperture bored through the wall of the hydraulic main or of any other main in the works. This eduction tube must at once descend, to allow liquids to flow into the flask, and must have a stopcock in it. The first member of the train is an empty dry thin glass flask C, which collects almost the whole of the spray, aqueous and tarry. DD are two stoppers for closing C hermetically, constructed of pieces of rubber tube closed at one end by short sections of glass rod. The bent wires by which these are permanently attached to the flask had better be of iron than of copper, as they are to be weighed with the flask, and the latter metal is quickly blackened and may be slightly changed in weight by the sulphide of ammonium that pervades the atmosphere of the gas-house. In a permanent apparatus, for nicety, platinum wires had better be used. Copper wires, however, used here, and in other parts of the apparatus, may be protected pretty well by coating with collodion, or even with a film of paraffine. [All the brass stopcocks I use in these and all other operations with sulphuretted gases, I prefer to plate, inside and out with nickel; which protects them perfectly against sulphur. This nickel-plating, every gas chemist will find it well worth his while to perform for himself, as it is very easy to accomplish, in case of brass and copper surfaces, with slight practice. I propose publishing a note which I think will lead any laboratory worker to success in his first trials.]

These trains of apparatus are probably most conveniently set up by being suspended to a strong wirebest of soft copper-stretched tightly between two convenient points of attachment. To make this wire tense or "taut," it had better be in two pieces, attached first at the extremities then twisted together strongly and warily with pincers at the point of meeting. The tubes are hung on inverted V-shaped (A) wires bent into hooks below. These, for simplicity, are not figured. All the

rubber tubing used as connectors, I wash laboriously, internally and externally, in a rapid current of water, with hard rubbing between the hands, until absolutely clean, then rub dry, and lubricate, within and without, with thick syrupy glycerine. The excess of this being wiped off, the tubing is found permanently more flexible, far less liable to abrasion of surface, more easily slipped over ends of glass tubing, and, above all, has its capacity for absorbing certain constituents of the gas reduced to a minimum. All the corks should be rubber, scoured and glycerated superficially in the same way. The cork at A-owing to the heat and actual contact with tar—and, to a less extent, the cork of flask C, are somewhat penetrated and softened, so that A gives out, after being used a number of times. The others last indefinitely.*

E and F are stuffed, uniformly, but as loosely as practicable, with cotton, which is best inserted and gently packed down, in successive small wads, picked out before insertion. The bulbous pattern, like E, † may present here some advantage, but it is not at all essential. Its use, as photographed in this case, was in order to bring down somewhat the level of the rest of the train. I have used, and prefer, a compound cotton apparatus, or two tubes of the size of F, united by a twisted wire in the manner of A in Fig. 4. These can be weighed together conveniently.

Even in case of a gas that has passed through condensers and scrubbers, it seems necessary to use two tubes of cotton. In one actual series of analyses, of unpurified coal gas before and after having passed the

* All these corks should be of the best quality made, Many in the American market are very poor-indeed useless for this kind of work. I procure mine from John N. Elmore (the successor of Quettier) at 193 Greenwich Street, New York; who will also supply, or have made, the different sizes and patterns of U tubes, etc.

I may say here that E, as shown in the cuts, was in the condition left after having been used, and in drawing from the photograph, an attempt has been made, none too successfully, to reproduce the shading of the condensed soot.

scrubbers and condensers, the second tube F, increased, on an average, in weight (all moisture having been removed) from the uncondensed gas 128 grain, and from the condensed 072 grain, per cubic foot of gas passed, up to seven cubic feet. The main consideration here is the initial pressure at command, of the gas. If the customary exhauster is employed in the gas works, and kept at work during the analyses, the pressure between the exhauster and the retorts may be found so low that a train attached between these, may not admit of more than one cotton tube, and even this packed as loosely as possible. At points beyond the exhauster, however, this trouble seldom occurs; it having been necessary indeed, in some such cases, with unpurified gas, to partially close the cock in the eduction tube, to bring down the rate of flow through the train to about one cubic foot per hour, which it should not in most cases exceed.

The Ammonia.-In order that we may employ, for dehydration, the highly convenient, powerful and reliable agent, chloride of calcium, it quickly became apparent to me, in my earliest experiments, that the ammonia must first be abstracted from the gas; and my first ef forts were to decide upon the proper agents that could be used, in solid form, for this absorption. One of these I have so far sufficiently tested, by quantitative as well as qualitative experiments, to demonstrate its entire applicability to this use; namely, fused potassic bisulphate. It is proper for me here to state that the earliest preliminary experiments with the bisulphate, were made, at my suggestion, in the course of an investigation carried on jointly by Prof. B. Silliman,* Dr. S. D. Hayes and myself; in which we desired to absorb the

* Prof. Silliman has also since worked by himself on this or a closelyrelated subject, and made a communication to the National Academy, at the late Philadelphia meeting, to which I would refer. Prof. S., I believe, experimented chiefly on the utilization of crude commercial bisulphates, generally of soda, called "salt-cake" in commerce, for the technical extraction of ammonia from gas.

ammonia of crude coal gas. We all became convinced, I believe, that potassic bisulphate had the power to take out qualitatively the NH3 from gas; but the precautions essential to success, in a quantitative way, have been since worked out by myself alone.

The mode of preparation of the bisulphate is by simply cracking in a mortar to the average size of wheat grains, and removing the dust and finer particles by a sieve of eight holes to the inch. The dust is very painfully irritating and injurious, and its inhalation must be avoided, if possible.

[Though many chemists seem somehow to have acquired the idea that bisulphate of potash possesses more or less deliquescence, it in reality has none of this quality whatever, and it is not even hygroscopic, to any remarkable extent.]

It must not be supposed that the bisulphate takes up ammonia as NH3, which would involve a very important error. The compound formed, as dessiccated for the final weighing, is the double sulphate of potash and oxide of ammonium. The factor am in the equations below must be obtained, from the increase of weight, by multiplying by a coefficient-70833. And it may here be remarked that a part of another factor wv comes likewise from this increase of weight, through multiplying it by 29267. This ammonia tube is lettered G.

The Water.-Chloride of Calcium for absorbing this, comes next in our Fig. 1 train, though, as it would be merely a duplicate of G, the CaCl tube has been omitted from the cut. I prefer-after trying many preparations -a fused chloride, assuring myself, above all, that it is free from every trace of causticity, and crack it up to the size of small peas, sifting out all that passes a sieve of six holes to the inch. For the small CaCl tube J, the one in M (Fig. 1), and J and L in Fig. 4, I find it desirable to crack but little, if any, smaller; to avoid risk of obstruction.

The Sulphuretted Hydrogen.-For this constituent I