LETTER TO DR. CRELL 265 



benzoin. 1 Lime-water is directed in the Swedish Pharma- 

 copoeia ; but in the original paper ( Transactions of the Royal 

 Academy), I have mentioned milk of lime ; for the particles 

 of the lime not only dissolve the acid of benzoin, but prevent, 

 in consequence of the boiling, the gum from adhering to it, 

 which happens when alkaline salts are employed. I have 

 by no means made use of the vitriolic acid for separating the 

 salt of benzoin, but have directed the muriatic acid for this 

 purpose ; and in this manner are flowers of benzoin prepared 

 here. 



There does indeed (as Mr. Gren afterwards observes) 

 take place a separation of mineral alkali when Glauber's 

 salt is boiled with unslaked lime. We obtain, however, but 



1 This observation comes from Mr. Greii of Bernburg, and is to the 

 following purport : 



Mr. Scheele's method of preparing flowers of benzoin, by boiling the 

 resin in lime-water, and then precipitating them with vitriolic acid, is 

 not without its difficulties, since the precipitated acid of benzoin is mixed 

 with the selenite that is produced, and it becomes necessary to separate 

 it by boiling water ; but the hot water that is requisite for this purpose, 

 dissolves a considerable quantity of the selenite, by which the salt of 

 benzoin is rendered impure. Mr. Gottling has therefore proposed 

 (Almanack for Chemists, 1782, p. 157) to use vegetable alkali instead of 

 lime-water ; no great advantage will result from this change, as long as 

 vitriolic acid is used for separating the salt of benzoin from the alkali, 

 as the vitriolated tartar is difficult of solution in cold water ; and there- 

 fore hot water must be used for the edulcoration of the salt of benzoin, 

 which at the same time dissolves a considerable portion of it. If, then, 

 the vegetable alkali is to be used for the extraction, it will be necessary 

 to use some other acid for the separation, in order to form a salt which 

 cold water will carry off by solution from the acid of benzoin. In order 

 to extract this acid, I use mineral alkali. I boil sixteen parts of benzoin 

 with two or three of the alkali, adding a sufficient quantity of water. I 

 then allow it to settle ; repeat the boiling with fresh alkali and water ; 

 filter the solution while it is hot, and evaporate it till it becomes a little 

 thick. After it has grown cool, I add vitriolic acid as long as any salt of 

 benzoin is seen to precipitate. I separate this salt by means of the filter 

 from the ley which contains Glauber's salt, and edulcorate it with cold 

 water. T. 



