289 



also be used with advantage for precipitating alkaloids which 

 yield precipitates of a more or less kermes-brown colour. 



/Sub-ci/anide of potassio-2}lcUimim [potassio-platinous cyanide], 

 (1 part in 19 parts water), gives well characterised precipitates 

 with some alkaloids. It is obtained by dissolving the grey-green 

 subchloride of platinum, obtained by heating the chloride, in an 

 aqueous solution of cyanide of potassium and by crystallising the 

 salt from the solution. 



Iodide of jjotassio-merairtj (2 parts chloride of mercury, and 5 

 pai'ts iodide of potassium in 43 parts water) yields with most 

 of the alkaloids insoluble precipitates. 



Iodide of potassiodnsmmtdi has been recommended recently as a 

 sensitive precij^itant of alkaloids. For this jnirpose it is prepared 

 by heating a mixture of 32 parts sxxlphide of bismuth, and 47^- 

 parts iodine, until xmder evolution of sulphur iodide of bismuth 

 has sublimated. Treat the siiblimate with a concentrated solution 

 of iodide of potassium hot as long as the latter dissolves anything, 

 decant the solution from the insoluble portion and mix with an 

 equal volume of a concentrated solution of iodide of potassium. 



Phosphate of soda, the common crystallised salt (1 part in 

 14 parts water), precipitates some alkaloids; it may also be used 

 instead of sulj)hate of soda, for removing lead from liquids, if the 

 introduction of sulphuric acid into the liquid has to be avoided. 



Phosplio-moljjhdate of soda (6 parts niolybdic acid, 12 parts 

 ciystallised carbonate of soda, and 1 pai-t crystallised j^hosphate 

 of soda in 3 1 parts water), mixed with pui-e nitric acid, until of a 

 pure citron-yellow colour. It precipitates alkaloids, and is highlv 

 important on account of it yielding preci}ntates with manv 

 alkaloids, which are not precipitated by other reagents. To fi'ee 

 these precipitates from other matters which may likewise have 

 been precipitated, washing with water must be avoided on account 

 of their liability to decompose. They are, therefore, treated in 

 the following way. Place the filter with its contents on several 

 thicknesses of blotting paper, and the whole on a new brickbat; 

 leave the precipitate until of a pasty consistence, transfer it then 

 to a porcelain dish and add water so as to form a thin pulp, 

 now add burnt magnesia under continual stirring, until every 

 trace of acid reaction has disappeared and a slightly alkaline 

 reaction towaixls litmus paper has taken its place, dry with a 

 gentle heat, grind the residue finely and shake with absolute 

 alcohol. Any alkaloid which has been liberated by the magnesia, 

 passes into the alcohol, remains on evaporating and may now be 

 subjected to a closer investigation. 



Phospho-tungstate of soda (10 parts tungstic acid, 12 parts crys- 

 tallised carbonate of soda, and 27 parts water are boiled until the 

 liquid is no longer precipitable by acids, i.e., until the tungstic 

 acid has passed into meta-tungstic acid ; add 1 part crystallised 



