122 Dr. Henry’s Analysis of several Varieties, &c. 
two equal quantities of sulphate of magnesia, it may be inferred 
that they contain no sulphate of soda,* For example, to de- 
cide whether the Scotch salt contains an alkaline sulphate, or 
not, I dissolved 1500 grains in a pint of boiling water, and eva- 
porated till fourteen drachm measures only remained, the 
common salt being removed as soon as it was formed. The 
residuary liquid was divided into two equal portions, one of 
which gave 18^ grains of sulphate of barytes, and the other, 
14 grains of ammoniacc-magnesian phosphate. The propor- 
tion between these numbers is so nearly that which has been 
already assigned, (viz. 112 to 90,) that we may safely infer 
the total absence of sulphate of soda. This salt, indeed, is 
considered as incompatible with muriate of magnesia ; but after 
digesting, for two or three days, 100 grains of the former, 
with 20 of the latter, evaporating to dryness, and washing the 
residuum with repeated affusions of alcohol, I found that two 
grains of the muriate of magnesia had escaped decomposition. 
* I employed more attention in investigating the presence of sulphate of soda in 
the products of sea water ; because this salt is stated to be one of its ingredients by 
the Bishop of Luanda ff, (Chemistry vol. ii. p. 62,) and by other chemical writers, 
Manchester, 
June 1 9, 1809. 
