APPARATUS FOR THE ANALYSIS OF GASSEg, QJ 



Its quantify, however, is very much influenced by the tern- Result much 

 perature employed. This remark, indeed, may be extended ^^hTaTem- 7 

 to all the aeriform products of coal; insomuch that from ployed, 

 equal weights of the same coal it is difficult to obtain by 

 different operations, conducted on a small scale, products 

 which are the same either in quantity or quality. The gas 

 from Coulbrooke dale tar, and that from caoutchouc^ have a 

 larger proportion of olehant gas, which in them amounts to 

 about one sixth of their bulk* 



2. Sulphuretted hidrogen gas is, also, most abundantly Sulphuretted 

 produced at the early stages of the distillation. Its pro- hldrc S eu * 

 portion then varies from 1 to 5 percent; and towards the 



close of the process it disappears entirely. It increases the 

 illuminating power of the coal gas; but is by no means a 

 desirable product; since it yields by combustion a gas (the 

 sulphurous acid) which is extremely offensive and irritating 

 to the lungs. By the distillation of coal, more sulphuretted 

 hidrogen is produced, than is discovered among the aeriform 

 products; for a part, uniting with the ammonia, which is 

 generated at the same moment, forms sulphuret of ammo- Sulphuretcf 

 nia, a compound which I have found among the condensed ammonia, 

 products. 



3. Carbonic acid gas, like the two preceding ones, ap- Carbonic acid* 

 pears only at an early stage of the process, and in small 

 proportion, never amounting to 5 per cent. A portion of 



this gas, also, unites with ammonia, and hence carbonate of 

 ammonia is found in the condensed fluid. 



4. The gas from coal undergoes a gradual diminution ofTheprodurt 



specific gravity and combustibility, from the commence- gradu f lly . di " 

 1 r> j . minishes m 



ment to the close of the process. This is best shown by gravity and 

 inspecting the results of the experiments on the Black* combustibility. 

 Mine and MertKyr coal gas in Table II, because they were 

 reserved in a greater number of separate portions than 

 usual. The progression would, perhaps, have been more 

 regular, in these as well as in the other instances, if much 

 of the gas had not been allowed to escape, in consequence 

 of the immense quantity which was produced. The speci- 

 fic gravity of the coal gas appears to afford a measure of its 

 fitness for illumination, sufficiently accurate fur practical 

 uses; but does not bear an exact correspondence to the 

 Vol,. XXII. Feb. 180Q. H chemical 



