31 



gas, the solutions from it always contain salts of iron, but they never 

 become of a blood-red colour until a mineral acid is added. When, 

 however, the solutions are evaporated, 'and the deliquescent residue is 

 exposed to the air, most, and sometimes all of the iron is peroxidized 

 and yields the well-known reaction. 



The nitrogen in tar may be shown from the spirit-solution off foul 

 clay. The spirit, evaporated to dryness and allowed to stand, de- 

 posits tar and a mixture of deliquescent crystalline salts. They were 

 aVowed to deliquesce, the fluid was removed, and the residual tar 

 well washed with water. Subsequently it was dissolved in hot spirit, 

 precipitated by water, and well washed. When nothing more was 

 removed by washing, the tar was heated, and evolved sulphide of 

 hydrogen and ammonia. Contrary to every other compound in gas 

 with which I have experimented, this tar gave off sulphide of hydro- 

 gen before ammonia. In other instances I have found the nitrogen 

 compound evolved at a lower temperature than the sulphur one. 



Mineral matter derived from the clay is found in all solutions ; but as 

 my object in this paper is to speak only of substances in gas, I pur- 

 posely omit those united with them derived from the clay. For the 

 same reasonl make no mention of the value of the foul clay as a manure. 



Sulphur compounds in gas purified so as not to affect basic 

 acetate of lead, and their removal. 



A recent Royal Commission on lighting picture galleries, has stated 

 the large quantity of sulphur found in some London gas, and has 

 intimated a doubt about the possibility of its removal. Dr. Letheby 

 concludes, from seven years' examination of gas in London, that 

 though quite free from sulphide of hydrogen, it contains, on an 

 average, 200 grains of sulphur in 1 000 cubic feet ; and Dr. Frank- 

 land, in the new edition of ' Ure's Dictionary of Arts,' part iv. pp. 

 730, 731, writes, "It is probable that volatile organic compounds 

 of sulphur are produced by the action of this element with carbon 

 and hydrogen simultaneously, although we have as yet no positive evi- 

 dence of their presence in illuminating gas When once generated 



with coal-gas, all attempts to remove these constituents have hitherto 

 proved ineffectual, and there seems little ground for hope that any 

 practicable process will be devised for their abstraction." I have 

 now the honour to submit evidence of the existence of these sul- 



