287 



soluble, wholly or partially, then the soluble portion contains 

 phosphoric acid. 



Chloride of calcium (1 part in 9 parts water) is used for 

 detecting a few acids through the formation of precipitates. The 

 latter, if newly precipitated, soluble in acetic acid, may contain 

 phosphoric acid; if not soluble, it contains oxalic acid. 



Acetate of lime (1 part in 9 parts watei*) is used for testing 

 oxalic acid instead of chloride of calcium, should the presence 

 of chlorides in the liquid have to be avoided. From liquids, 

 containing acetates only, or free acetic acid, the oxalic acid can be 

 removed entirely by means of the above reagent. 



Chloride of iron [perchloride of iron] (1 part in 9 parts water) 

 indicates the various tannic acids by yielding blue or green 

 precipitates of various gi'adations of colour, or similarly coloured 

 liquids; though a green tinge, produced by chloride of iron, must 

 not be taken as satisfactory proof of the presence of tannin. 

 Gum arable also is precipitated by the reagent. 



Sub-sulphate of iron, or gi-een vitriol (1 part in 9 parts water), 

 is sometimes used for testing tannic .acids instead of chloride 

 of iron, as the colours of the precipitates, produced by these two 

 iron salts, differ sometimes considerably. 



Glue (1 part isinglass in 100 parts alcohol of 40%) is the 

 test of the true tannic acids, with which it yields insohible or 

 hardly soluble, and mostly grey and flocky, precipitates. 

 Should the solution of glue prove too thick, it must be heated 

 gently and shortly before use (not diluted with water or with 

 alcohol). 



To remove tannic acid from liquids which contain other acids 

 isinglass is used, in small narrow strips previously soaked in cold 

 water. 



Tartarate of antimony and j)otash [tartar emetic or tartarated 

 ■antimony\ (1 part in 19 parts water) precipitates most of 

 the tannic acids, and may therefore be used for testing these as 

 an accessory reagent. 



Acetate of lead [sugar of lead] (1 pai-t in 9 parts water), 

 the most important chemical in phyto-analyses used as pre- 

 cipitating and separating agent; it precipitates completely 

 sulphuric and phosphoric acids, and more or less completely most 

 of the oi'ganic acids, pigments, protein-substances, and resins. 

 Those anorganic lead-precipitates are insoluble in acetic acid; 

 most of the others are soluble. 



Trihasic acetate of lead [lead-vinegar or siibacetate of lead] (of 

 1'200 specific gravity). — After a vegetable exti-act has been 

 precipitated by acetate of lead, a new precipitate is generally 

 formed on addition of lead-vinegai", but instead of using at once 

 the latter, it is preferable and more convenient to saturate the 

 acid liquid containing yet acetate of lead, first with ammonia, and 



