SECONDARY PRODUCTS. 201 



siphon are the most valuable, and are those which Mr. Lowe more especially 

 refers to when speaking of the spirit of coal-tar. 



Although the cost of the above spirit is very trifling, I much prefer the use 

 of native naphtha for the purpose of impregnating the coal-gas, since it has a 

 less offensive odour. This last substance oozes out of several rocks, as sand- 

 stone, slaty clay, etc., or is found on the surface of springs and other waters, 

 in various districts of Italy ; in Sicily, Zante, the Caspian Sea ; in Persia and 

 other countries in Asia ; also in Westphalia and Alsace : it is an article of 

 commerce, and is used by varnish manufacturers, of whom it may be pur- 

 chased. 



Coal-tar yields inflammable gas in great abundance*, of a high specific 

 gravity: on one occasion I procured it as high as '710. It is seldom lower 

 than "650. From this circumstance engineers have been induced to submit 

 the tar obtained in their first process of forming coal-gas to a second 

 distillation, with an intention of improving the quality of the first products. 

 The form of apparatus used is similar in construction to that for procuring 

 gas from oil. If it could be stored and burnt, separately from the coal gas, 

 in lamps made on purpose, it might be found to answer ; but the expense and 

 trouble attending its formation renders the use of it, independent of other cir- 

 cumstances, objectionable. 



Experiments have been tried by pouring tar upon the charge of coal before 

 being introduced into the retort. If the gases formed by these substances 

 would unite chemically, and the combustion of them be equally effected, the 

 process doubtless would be ceconomical ; but they do not unite : they are two 

 distinct compounds, possessing different properties, and having no affinity for 

 one another under ordinary circumstances ; therefore this operation has always 

 failed to produce the desired end. 



I decidedly think that the most ceconomical use to which coal-tar can be 

 applied, is to burn it beneath the retorts, as directed in another part of this 

 volume. 



AMMONIACAL LIQUOR. 



IF the properties of manure, and its agency upon the growth of the vegetable 

 world, can be explained by chemistry, we shall find the ammoniacal liquor 



* 112 Ibs. of coal-tar yield upon an average 1000 cubic feet of gas of the specific gravity 

 650. 



