])r. Sclmnck on the Formation of Indigo -blue. 129 



f'ormiate of lead there are contained by calculation 75'11 paits 

 of oxide of lead. 



The liquid poured off from these crystals was mixed with an 

 excess of sulphuric acid, filtered from the sulphate of lead and 

 distilled. The distilled liquid was boiled with peroxide of mer- 

 cury, in order to decompose any formic acid which it might con- 

 tain, and filtered, and after sulphuretted hydrogen had been 

 passed through it, it was again filtered from the precipitated sul- 

 phuret of mercury. The excess of sulphuretted hydrogen was 

 removed by agitation with carbonate of lead, and the filtered liquid 

 was mixed with an excess of sulphuric acid, filtered again from 

 the sulphate of lead and distilled. The distillation was repeated, 

 and the distillate was then boiled with carbonate of silver, fil- 

 tered and evaporated in vacuo. A residue was left consisting of 

 small white crystalline grains, which repelled water just as if 

 they contained fatty matter. When a portion of this residue 

 was mixed with alcohol and sulphuric acid and the mixture was 

 boiled, a smell like that of butyric sether was given off. The 

 quantity obtained was just sufficient for one analysis, the results 

 of which were as follows : — 



0-4120 grm. gave 0-2370 grm. carbonic acid and 0-0925 

 water. 



0-0990 grm. gave 0-0835 grm. chloride of silver. 



These numbers correspond in 100 parts to — 



Carbon 14-62 



Hydrogen 2-32 



Oxygen 14-87 



Oxide of silver 68-19 



100-00 

 This composition approximates, as will be seen, to that of 

 acetate of silver, which consists in 100 parts of — 



Carbon 14-37 



Hydrogen 1-79 



Oxygen 14-38 



Oxide of silver 69-46 



10000 

 The excess in the amount of carbon and hydrogen, and the 

 deficiency in that of the oxide of silver, show, however, that it must 

 have contained a small quantity of the silver salt of another acid 

 belonging to the same series as formic and acetic acids, a series 

 having the general formula C" H" O**. This acid was probably 

 propionic acid, an acid the formation of which must indeed be 

 assumed in order to explain how one of the other products of de- 

 composition of indican takes its rise. The quantity of this acid, 

 rial. Mag. S. 4. Vol. 15. No. 98. Feb. 18.-)8. K 



