in the Isle of Wight, 237 



phosphat became slightly brownish during the calcination, owing to 

 the presence of a few particles of iron, the quantity of which was 

 too minute to be ascertained. 



§ Xlir. Precipitation of the sulphuric and ?nuriatic Acids ^ with 

 a view to ascertain their Quantity. 



Before drawing any ultimate conclusion respecting the contents of 

 the water and the proportions of its ingredients, I found it necessary 

 to ascertain the quantities of sulphuric and muriatic acids which it 

 contained, in order to enable me to try how far these quantities 

 might coincide with the conclusions obtained by the separation of 



white opaque vitreous globule, without any further diminution of weight. In its friable 

 state it was readily dissolved by muriatic acid ; in its vitrified form it required heat and 

 trituration. This salt was perfectly tasteless and shewed no attraction for water. With 

 regard to the proportions of acid and base to be inferred from this experiment, it is ob- 

 vious that if 30,8 grains of phosphat of magnesia contain 11,82 grs. of earth, the 

 remainder, viz. 18,98 grs. represents the proportion of phosphoric acid 5 which is 

 equivalent to 38,37 grs. of magnesia, in 100 of phosphat. In another experiment con- 

 ducted in a similar manner, the magnesia amounted to 38,7 grains, so that by taking the 

 mean between these two very nearly similar results, we have the following propor- 

 tions, viz. 



]\Iagnesia . 38,5 > . .,..,,,. 



~ Phosphoric acid 61,5 \ '" ^°^ S""^'"' "^ 'S"'*^'^ P^^^P^^* «f magnesia. 



We may infer therefore that one grain of phosphat of magnesia, the quantity yielded 

 fay the twenty grains of residue, indicated 0,383 of pure magnesia ; and if, according to 

 the statements of Kirwan and Wenzel (which very nearly agree) one hundred grains of 

 crystallized sulphat of magnesia contain seventeen grains of magnesia, 2,26 grains of that 

 salt will be the quantity corresponding to 0,385 graius of magnesia. And I have the 

 satisfaction of observing that the proportions obtained by Dr. Henry, of one hundred 

 grains of ammoniaco-magnesian phosphat dried at 20°, for one hundred and eleven grains 

 of crystallized sulphat of magnesia, would have led to a very similar result. (See De, 

 Henry's ' Analysis of several varieties of Saltj' in Philos. Trans, for 1810, page 113:) 



