546 GAS, COAL 



bonic acid from coal-gas depends. On passing coal-gas containing this acid through 

 slaked lime in fine powder, or through milk of lime, the whole of the carbonic acid 

 disappears, having united with the lime. Quick-lime, slaked in such a manner as to 

 bo neither dust-dry nor very perceptibly moist, is most effective for the absorption of 

 high percentages of carbonic acid, a layer three inches in thickness not allowing a 

 trace of the acid gas to pass through it. 



The presence even of a small percentage of carbonic acid in coal-gas is much to bo 

 deprecated, on account of the great loss of light which it occasions, 1 per cent, of 

 carbonic acid diminishing the illuminating power of coal-gas to the extent of about 

 6 per cent. ; the addition which it makes to the carbonic acid produced during combus- 

 tion is, however, too minute to be of any importance. 



Carbonate of ammonia. During the destructive distillation of coal, a considerable 

 proportion of the nitrogen contained in the coal is converted into carbonate of am- 

 monia, the greater part of which condenses in the aqueous layer of liquid products ; 

 but as carbonate of ammonia is very volatile, even at ordinary temperatures, crude 

 coal-gas always contains a small quantity of this compound. It is a volatile, white, 

 crystalline solid, very soluble in water, and possessing a pungent smell like ammonia. 

 Its vapour is decomposed by lime, which unites with carbonic acid, liberating am- 

 monia. The presence of this salt, or of ammonia, in coal-gas is very undesirable, as it 

 corrodes brass fittings, and is also partially converted into nitrous acid during the 

 combustion of the gas. 



Bisulphide of Carbon. This compound consists of 6 parts, by weight, of carbon, 

 and 32 parts of sulphur ; it is formed whenever sulphur and carbonaceous matter are 

 brought together at a bright red heat, and therefore, owing to the presence of sulphur 

 in all varieties of coal, its vapour is generally, and probably always, present in coal- 

 gas. Bisulphide of carbon is a colourless liquid, of a most insupportable odour re- 

 sembling garlic ; it is very volatile, boiling at 108. It does not mix with water, 

 but dissolves in alcohol and ether ; it is also very soluble in solution of caustic soda 

 or potash in methylic, ethylic, or amylic alcohol. It is very inflammable, and generates 

 during combustion much sulphurous acid ; on this account its presence in coal-gas is 

 very injurious, and as there has hitherto been no known means of removing it on a 

 largo scale by any mode of purification, its non-generation in the process of gas- 

 making becomes a problem of great importance. Few attempts have yet been made 

 to solve this difficulty, but Mr. Wright, the eminent engineer of the Western Gas 

 Company, has observed that its formation is greatly hindered, if not entirely prevented, 

 by the employment of a somewhat moderate temperature. In corroboration of this 

 .observation it* has frequently been noticed that the gas furnished by companies who 

 use a high heat contains a very large quantity of this noxious material, whilst gas 

 generated at lower temperatures, as for instance, that produced by White's hydro- 

 carbon process, contains mere traces of this compound. Although no process for the 

 absorption of bisulphide-of-carbon vapour from coal-gas is sufficiently cheap for em- 

 ployment on a large scale, yet advantage might be taken of its solubility in a solution 

 of caustic potash in fusel oil (a by-product in spirit distilleries), or in methylated 

 spirit of wine, for its removal from the gas supplied to private houses, where the 

 damage done by the sulphurous acid is most annoying. By passing the gas over a 

 considerable surface of this solution, contained in a small private purifier, the bisul- 

 phide-of-carbon vapour is completely removed. 



A method of removing bisulphide of carbon from coal-gas has, however, been 

 recently suggested by Mr. Vcrnon Harcourt, F.R.S. This chemist found that when 

 impure gas was passed through an iron tube, 3 inches in diameter, filled with iron 

 turnings and heated to low redness for a length of about two feet, the amount of 

 bisulphide of carbon could be so far reduced that the pas, after purification from 

 sulphuretted hydrogen, contained only 5 or 6, instead of about 30 cubic inches, in 100 

 cubic feet. A yet greater reduction in the amount of sulphur may be effected by 

 heating the gas after, instead of before, purification, and then purifying the product a 

 second time. In these experiments the sulphur of the bisulphide of carbon combines 

 with hydrogen, perhaps with the aid of watery vapour, and forms sulphuretted 

 hydrogen, which can be readily removed by the ordinary methods. Under certain 

 circumstances, it appears that the illuminating power of the gas is actually increased 

 by this process of heating to remove the bisulphide of carbon. 



Bisulphide-of-carbon vapour can be readily detected in coal-gas by a very simple 

 apparatus devised by Mr. Wright ' ; in this instrument the products of the combustion 

 of a jet of gas are made to pass through a small Liobig's condenser ; if the liquid 

 dropping from this condenser strongly redden blue litmus paper, it is highly probable 



I 



; This instrument can be had on application to Mr. Wright, 60 and 65A Millbank Street, West- 

 minster, B,W. 



