176 Analysis of several Varieties of 



the sulphate of barytes (C. b.) the proportion of 74 to l1$ f 

 or very nearly so, we may infer, that no other sulphate id 

 present but that of lime. The same conclusion will tal- 

 low, if, after having decomposed one half of the watery 

 solution (C.) by muriate of barytes, and another half by 

 oxalate of potash, we find that the sulphate of barytes bears 

 to the oxalate of lime, the proportion of 175*9 to 102*5. 

 Now these proportions were, as nearly as could be ex- 

 pected, obtained in ibe analysis of North wich salt; from 

 tvhence we mav conclude, that the only sulphate which it 

 contains is gypsum, or the sulphate of lime 



It must be remembered, however, that the calcareous 

 sulphate, contained in any variety of common salt, cannot 

 be in a state of complete desiccation, but. would lose 22 

 parts out of 100, bv 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 obtained 

 by the foregoing rule, or, more simply, to assume that 10O 

 grains of sulphate of barytes indicate 73 grains of sulphate 

 of lime, dried at 3 60° Fahrenheit, =57 ignited. 



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

 were both ascertained, and other sulphates also might pos- 

 sibly 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 processes D. &c.) I estimated how much sulphate of 

 barvtes they ought respectively to afford ; and then com- 

 pared 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 digested with alcohol, were converted into 31 grains 

 of calcined sulphates, consisting of 19 grains of dry sul- 

 phate 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 difference much 

 too trivial to be admitted as an indication of any sulphate 

 with an alkaline base; and arising, probably, from un- 

 avoidable errors in the experiment. 



* This I find to be the loss sustained by 100 grains of artificial selenite, 

 dried at 160°, 'and then ignited. The same quantity of crystallized native 

 selenite, 1 learn from Dr JNIarcet, loses 20-7 grains, by being calcined in a 

 strong red heat. 



(F.a.) 



