UMATION OF INDIGO-BLUE. 219 



an excess of carbonate of soda and evaporated to dry- 

 The saline residue was mixed with an excess of dilute 

 sulphuric acid and the liquid was distilled. The distillate was 

 now colourless. It contained formic acid, for after being neu- 

 tralised and mixed with nitrate of silver, metallic silver was 

 soon deposited even in the cold. The whole of it was boiled 

 with carbonate of lead, and the filtered liquid was evaporated, 

 when it yielded some shining crystalline needles surrounded 

 by a thick syrup. By means of a little cold water the syrup 



removed, the needles being left undissolved. The latter 

 had the properties of formiate of lead. 



0.3450 grm. of these needles dried at 100° C. and heated 

 with sulphuric acid gave 0.3505 grm. sulphate of lead, equi- 

 valent to 0.2579 oxide of lead or 74.75 per cent. In 100 

 parts of formiate of lead there are contained by calculation 

 75.11 parts 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 mercury, in order to decompose any formic acid which it 

 might contain, and filtered, and after sulphuretted hydrogen 

 had been passed through it, it was again filtered from the 

 precipitated sulphuret of mercury. The excess of sulphu- 



d hydrogen was removed by agitation with carbonate of 

 lead, and the filtered liquid was mixed with an excess of sul- 

 phuric acid, filtered again from the sulphate of lead and dis- 

 tilled. The distillation was repeated and the distillate was 

 then boiled with carbonate of silver, filtered and evaporated 

 in vacuo. A residue was left consisting of small white crys- 

 talline 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 



that of butyric ether was given off. The quantity ob- 

 tained was just sufficient for one analysis, the results of which 

 were as follows : — 



