322 Dr. Stenhouse's Examination of Purree^ the substance 



which chiefly consist of magnesia. The ashes also contain 

 some potash in the state of carbonate, and a little lime, but no 

 phosphoric acid. Purree dissolves very readily in most acids. 

 The one which I usually employed was the acetic^ in which, 

 when assisted by heat, it is exceedingly soluble. The colour 

 of the solution is a deep reddish-brown ; on cooling it depo- 

 sits a quantity of dark brown flocks, and on standing for a few 

 days a quantity of deep yellow crystals arranged in small stars 

 appear in the liquid, the taste of which is exceedingly nauseous. 

 The most convenient way of obtaining these crystals in a pure 

 state is the following: — 



Dissolve the purree, cut into small pieces, in boiling water 

 containing a considerable quantit}' oF acetic acid, and filter 

 the liquid to remove the insoluble matter, which consists 

 chiefly of dark brown flocks and of some other impurities. 

 The clear liquid is to be treated with a solution of acetate of 

 lead so long as it occasions a precipitate, which is very bulky 

 and has a brownish-yellow colour. The precipitate is to be 

 collected and washed with cold water, and to be decomposed 

 by sulphuretted hydrogen ; it is then to be repeatedly boiled 

 with spirits of wine, in which the yellow crystals are pretty 

 soluble. On the cooling of the liquid the crystals are depo- 

 sited in great quantity ; they are long flat needles arranged in 

 stars, and have a deep yellow colour and considerable lustre. 

 They redden litmus pretty strongly, and consist of a vegetable 

 acid united in the crude substance (purree) with magnesia. 

 They are still far from pure, and retain a considerable quan- 

 tity of magnesia, from which it is extremely difficult to free 

 them. The crystals should then be dissolved in a hot solution 

 of carbonate of soda and filtered. When the solution is neu- 

 tralized with muriatic acid, they are again deposited on the 

 tooling of the liquid. The crystals should be collected, washed 

 with cold water, in which they are very slightly soluble, to re- 

 move adhering muriatic acid, and dried by pressure. They 

 should again be dissolved in hot water and be precipitated by 

 acetate of lead. The lead salt should then be decomposed by sul- 

 phuretted hydrogen, and the crystals dissolved out by hot spi- 

 rits of wine. The crystals have now only a faint shade of yellow, 

 and are to be still further purified by being five or six times 

 crystallized from spirits of wine. They are then almost en- 

 tirely pure, though on being burned on platinum foil they still 

 leave a mere trace of magnesia, so small as to be scarcely per- 

 ceptible. I was not able to remove this minute portion of mag- 

 nesia, even by repeatedly crystallizing the acid from aether. 



I. 0-3975 grm. substance dried at '212° F. and burned with 

 chromate of lead, gave 0*7979 carbonic acid and 0*1583 water. 



