ANALYSIS OF BRITISH AND FOREIGN SALT. 279 



that the sulphate of barytes bears to the oxalate of lime the Separation and 

 „ -»-,. , , • calculation of 



proportion of 175\9 to 102*5. Now these proportions were, the earthy suU 



as nearly as could be expected, obtained in the analysis of phates. 



Northwich salt ; whence we may conclude, that the only 



sulphate, which it contains, is gypsum, or the sulphate of 



lime. 



It roust be remembered, however, that the calcareous 

 sulphate, contained in any variety of common salt, cannot 

 be in a slate of complete desiccation, but would lose 22 

 parts out of 100, by exposure to a red heat*. It becomes 

 necessary, therefore, either to increase, in the proportion of 

 5 to 4, our estimate of the sulphate of lime obtaine4 by the 

 foregoing rule, or, more simply, to assume, that 100 grains 

 of sulphate of barytes indicate 73 grains of sulphate of 

 lime, dried at l60° Fahrenheit, zr 57 ignited. 



(F.) When sulphate of lime and sulphate of magnesia 

 were both ascertained, and other sulphates also might possi- 

 bly be present, as in the varieties of salt from sea water, the 

 calculation became a little more complicated. In this case, - 

 after determining the quantity of both sulphates, (by the pro- 

 cesses D. &c.) I estimated how much sulphate of barytes 

 they ought respectively to afford ; and then compared the 

 estimated quantity with that which was actually obtained. 

 The earthy carbonates, for example, precipitated from 1000 

 grains of Lymington salt, which had previously been di- 

 gested with alcohol, were converted into 31 grains of cal- 

 cined sulphates, consisting of 19 grains of dry sulphate of 

 magnesia, and 12 grains of dry sulphate of lime. Now 

 from the magnesian sulphate 38 grains of sulphate of 

 barytes should result; and from the sulphate of lime 21 

 grains; the sum of which is 59. But the quantity actually 

 obtained was 59'8. There is only, therefore, an excess of 

 0*8 grain of the actual above the estimated quantity, a dif- 

 ference much too trivial to be admitted an indication of 

 any sulphate with an alkaline base; and arising, proba- 

 bly, from unavoidable errours in the experiment. 



* This I find to be the loss sustained, by 100 grains of artificial «c- 

 lenite, dried at l6o°, and then ignited. The same quantity of crys- 

 tallized natire selenite, I learn from Dr. Marcet, loses 207 grains, by 

 fceiug calcined in a strong red heat. 



(F, a.) 



