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ACETYLENE 39 formation of lime and acetylene, while, if there be suf- cesses of purification as will render it harmless and inficient water present, the lime combines with it to form nocuous to health and property, and the sooner calcium hydrate. it is recognized as absolutely essential to purify Pyritica1. Calcium carbide. Water. Acetylene. Lime. acetylene before consuming it the sooner will t,oa' CaC2 + H20 = C2H2 -f- CaO. the gas acquire the popularity it deserves. The only one Lime. Water. Calcium hydrate. of the impurities which offers any difficulty in removal is CaO + H20 = Ca(HO)2. the. phosphuretted hydrogen. There are three substances Every operation, no matter how simple it appears at which can be relied on more or less to remove this comfirst sight, is capable of being performed in several ways, pound and the gas to be purified maybe passed either and decomposition of the carbide by water may be brought through acid copper salts, through bleaching powder, or about either by bringing the water slowly into contact through chromic acid. In experiments with these various with an excess of carbide, or by dropping the carbide into bodies it is found that they are all of them effective in an excess of water, and these two main operations again also ridding the acetylene of the ammonia and sulphuretted may be varied by innumerable ingenious devices by which hydrogen, provided only that the surface area presented the rapidity of the contact may be modified or even to the gas is sufficientiy large. The method of washing eventually stopped. The result is that although the forms t re gas with acid solutions of copper has been patented of apparatus utilized for this purpose are all based on the by Herr A. Frank of Charlottenburg, who finds that a one fundamental principle of bringing about the contact concentrated solution of cuprous chloride in an acid the Oi the carbide with the water wdiich is to enter into double liquid being made into a paste with kieselgiihr, is the decomposition with it, they have been multiplied in number most effective. Where the production of acetylene is to a very large extent by the methods employed in order going on on a small scale this method of jiurification is to ensure control in working, and to get away from the undoubtedly the most convenient one, as the acid present dangers and inconveniences which are inseparable from a | absorbs the ammonia, and the copper salt converts the too rapid generation. ■ phosphuretted and sulphuretted hydrogen into phosphates In attempting, to classify acetylene generators some and sulphides. The vessel, however, which contains this Generaauthorities have divided them into as many as mixture has to be of earthenware, porcelain, or enamelled sx tors. ^ different classes, but this is hardly necessary, iron on account of the free acid present; the gas must be as they may be divided into two main classes :— washed after purification to remove traces of hydrochloric first,, those in which water is brought in contact with the acid, and care must be taken to prevent the complete carbide, the carbide being in excess during the first portion neutralization of the acid by the ammonia present in the of the operation; and, second, those in which the carbide g The second rocess one patented Ullmann is thrown into water, the amount of water present bein°- ofT'n Geneva, who Putilizes ischromic acid by to Dr oxidize the always in excess. The. first class may again be subdivided phosphuretted and sulphuretted hydrogen and absorb the into generators in which the water rises in contact with ammonia. The third process owes its inception to Lunge, the. carbide, in which it drips upon the carbide, and in I uho recommends the use of bleaching powder. Dr Wolff which a. vessel full of carbide is lowered into water, and has found that when this is used on the large scale there again withdrawn as generation becomes excessive. Some is a risk of the ammonia present in the acetylene forming of these generators are constructed to make the gas only traces of chloride of nitrogen in the purifying boxes, and as fast as it is consumed at the burner, with the object of as this is a compound which detonates with considerable saving the expense and room which would be involved by local force, it occasionally gives rise to explosions in the a storage-holder. Generators with devices for regulating purifying apparatus. If, however, the gas be first passed and stopping at will the action going on are generally through, a scrubber so as to wash out the ammonia this termed “automatic.” Another set merely aims at develop- danger is avoided. Dr Wolff employs purifiers in which ing the gas from, the carbide and putting it into a storaou- the gas is washed with water containing calcium chloride, holder with as. little loss as possible, and these are termed and then passed through bleaching powder solution or non-automatic.” The points to be attained in a good other oxidizing material. generator are:— When acetylene is burnt from a 000 union jet burner at all ordinary pressures a smoky flame is obtained, but 1. Low temperature of generation. 2. Complete decomposition of the carbide. on the pressure being increased to 4 inches a magnificent 3. Maximum evolution of the gas. name results, free from smoke, and developing an illuminat4. Low pressure in every jiart of the apparatus. ing value of 240 candles per 5 cubic feet of gas consumed, 5. Ease in charging and removal of residues. olightly higher values have been obtained, but 240 may 61110 Va a r rom ie a a the gas ^ ^ ^ ^ PP ratus before generation of be taken as the average value under these conditions When acetylene was first introduced as a commercial . ^ ^en carbide is acted upon by water considerable heat diummant m England, very small union jet nipples were is evolved , indeed, the action develops about one-twentieth utilized for its consumption, but after burning of the heat evolved by the combustion of carbon. As, for a short time these nipples began to carbonize IUum'aau owever, the temperature developed is a function of the the flame became distorted, and then smoking ingpowertime needed, to complete the action, the degree of heat Wlth tlle fomiation of attained varies with every form of generator, and while rTf, a heavy deposit of soot. U hile these troubles were being experienced in England, the water in one form may never reach the boiling-point, attempts had been made in America to use acetylene the carbide in another may become red-hot and give a diluted with a certain proportion of air which permitted it temperature of over 800J C. Heating in a generator is to be burnt in ordinary flat flame nipples : but not only a source of danger, but also lessens the yield of the danger of such admixture being recognized, Buraers’ gas and deteriorates its quality. The best forms of nipples of the same class as those used in England were generator are either those in which water rises slowly in employed, and the same troubles ensued. In France, contact with the carbide, or the second main division in single jets made of glass were first employed, and then which the carbide falls into excess of water. tisener, Luchaire, Ilagot, and others, made burners in It is clear that acetylene, if it is to be used on a large v rich two jets of acetylene, coming from two tubes placed scale as a domestic illuminant, must undergo such pro- some little distance apart, impinged and splayed each other