ANALYSIS OP BRITISH AND FOREIGN SALT. 577 



The sulphate of barvtes was then washed sufficiently; dried, Separation and 



-j , . . • , calculation of 



ignited, and its amount ascertained. lhe eatt hj su j. 



To the earthy carbonates an excess of sulphuric acid was phates. 

 added in a platina dish, and the mixture was triturated, till 

 all effervescence ceased. It was then evaporated to dryness, 

 calcined in a low red heat, and the weight of the earthy sul- 

 phates was ascertained. « 



(D. a.) The dry sulphates were washed with a small 

 quantity of lukewarm water. In several instances, the loss 

 of weight, thus sustained, was extremely trifling, nothing 

 being dissolved but a very minute portion of sulphate of 

 lime, of which earthy salt, solely, the residue was presumed 

 to be composed. 



(D. b.) But in other cases, a considerable loss of weight 

 ensued; and in these, to the watery solution was addefl a 

 mixture of equal parts of saturated solutions of carbonate 

 of ammonia, and phosphate of soda. A precipitate more 

 or less copious was produced, which was collected, dried at 

 90° Fahrenheit, and weighed. 



(D. c.) By direct experiments I had determined, that 00 

 grains of this precipitate result from the decomposition of 

 100 grains of sulphate of magnesia, of such a degree of 

 dryness, as to lose 44 grains out of 100, by exposure to a 

 )*>w red heat, Hence 100 grains of ammoniaco-magnesian 

 phosphate indicate 111 grains of crystallized, or 62*2 of 

 desiccated, sulphate of magnesia*. From the weight of the 

 ammoniaco-magnesian phosphate, it was easy, therefore, to 

 infer the proportion of sulphate of magnesia in any mixture 

 qf the two earthy sulphates, 



(D. d.) It was possible, however, that, in addition to the 

 sulphates of lime and of magnesia, the quantity of which 

 had been determined by the foregoing process, the speci- 

 men of salt under examination might contain also an alka- 

 line sulphate, To decide this point, it was necessary to 



* The assumption, that crys'allized sulphate of magnesia contains <vr * f 

 only 44 per cent of water, though it was correctly true with the sped- crystallisation 

 men on which I operated, is below the average j which, I find from in sulphate of 

 several experiments, is about one half the weight of the eak, Mr. ma g n e=ia> 

 Jvirwau states the water of crystallization to be 53 0* in 100 grains ; but 

 this, I believe, a little exceeds the truth. 



-compare 



