290 



phosphate of soda, restore the water lost by evaporation, and filter 

 if necessary). After it has been strongly acidified by nitric acid, 

 it acts similar to phospho-molybdate of soda, and is even more 

 sensitive towards some alkaloids. In all other respects, what has 

 been said of the preceding reagent is applicable to this one too. 



Picric acid yields with many alkaloids yellow and mostly 

 crystalline precipitates. 



Chloride of 2)latinum [platinic chloride] (1 part in 19 parts 

 water) is one of the most common precipitants of alkaloids. The 

 precipitates are various shades of yellow, flocky, and distinguish- 

 able hereby from those obtained by ammonia or potash, which are 

 pulverulent or crystalline. 



Chloride of mercury [mercuric chloride] (1 part in 19 parts 

 water). Precipitating reagent of alkaloids, and forming a white 

 double-compound ; but several of which are rather soluble in 

 water, and do therefore not appear in diluted solutions. 



Chloride of mercury forms also with protein substances com- 

 pounds which do not dissolve in water. 



Sub-nitrate ofjxdladitcm [palladious nitrate] (1 part in 19 parts 

 water). Precipitant of alkaloids. The compounds are yellow or 

 brown. 



Sub-nitrate of mercury [mercurous nitrate] (1 part in 19 parts 

 water under addition of a few drops of nitric acid). As in general 

 vegetable extracts contain compounds of chlorine, a turbidity is 

 nearly always occasioned by this test, and which cannot be 

 removed by nitric acid. It precipitates also most of the organic 

 acids, but tlie precipitates are mostly decomposed partially on 

 keeping, changing their (as a rule) white colour into a grey one. 

 Even if no precipitate has been obtained, the liquid, containing 

 organic matters, often assumes with this reagent a grey or a 

 darker colour, produced by the reduction of the sub-oxyd of mer- 

 cury, and indicating eventually gallic acid, which acts strongly 

 reducing on this salt. 



Nitrate of silver (1 part in 19 parts water) yields with some 

 alkaloids sparingly or not at all soluble double compounds, which 

 separate as white, flocky precipitates. In other i-espects, all that 

 has been said of the sub-nitrate of mercury applies also to this 



^est. As regai-ds its application for the quantitative estimation of 



formic and of hydrocyanic acids, I refer to these substances in the 

 first division of the first part of this work. 



The following substances are not employed for testing, but for 

 separating and purifying: — 



Oxyd of lead, ground to a subtle powder, serves for removing 

 tannic acid from liquids or from pulpy precipitates. Mix the 

 latter intimately with the oxyd of lead, dry, grind the remnant 

 and withdraw from it the other constituents (usually an mdifierent 

 or a basic bitter substance) by means of alcohol. It may be some- 



