TRANSACTIONS OF THE SECTIONS. 49 



Having exposed a quantity of gradually dried phosphate of soda to a 

 bright red heat, he weighed out 30 grains while nearly red hot, dis- 

 solved it in water, and added to it a solution of 83 grains of crj'stals 

 of nitrate of lead, — proportions equivalent to those which Dr. Thom- 

 son used, and half the numbers which are generally used to indicate 

 the atomic weights. The mixture was well agitated ; a precipitate 

 of phosphate of lead formed, which was washed, dried, exposed to a 

 low red heat, and weighed ; the liquor from which it was separated gave 

 a precipitate of sulphate of lead by the addition of sulphate of potash. 

 The mean of four nearly agreeing experiments gave phosphate of lead 

 66*96 grains, and sulphate of lead 4"42 grains. Now 4"42 sulphate of 

 lead = 4-82 nitrate of lead ; and 83 — 4-82 = 78-18 nitrate of lead 

 spent in producing the precipitate of phosphate. 



The acid in 78-18 nitrate of lead being capable of neutralizing 15-07 

 soda, and the liquor when freed from lead by sulphate of potash being 

 neutral to the litmus test, it follows that 30 grains of anhydrous pyro- 

 phosphate of soda are constituted of 15-07 soda and 14-93 acid ; and 

 the atoDodc weight of soda being 32, that of the acid in pyrophosphate 

 of soda must be 31-7. 



One hundred grains of the crystals of the ordinary phospate of soda, 

 by being placed under the exhausted receiver of an air-pump with a ves- 

 sel of sulphuric acid, are reduced to 39-65 grains; and the residue, by 

 exposure to a red heat, is reduced to 37-1 grains. From this and the 

 result of the above-mentioned experiments Mr. Watson infers that the 

 quantity of soda in 100 grains of crystals of the ordinary phosphate is 

 18-63 grains, and that the quantity of acid is 18-47 grains. 



Mr. Watson ha^dng decomposed both the ordinary uncalcined phos- 

 phate of soda and thepyrophosphate with lime water, found that the quan- 

 tity of lime which sufficed to saturate a proportion of the latter was not 

 sufficient to saturate a corresponding proportion of the former. From 

 this and other circumstances of the analysis Mr. Watson is led to sus- 

 pect that the phosphate of soda when dried as much as possible in the 

 exhausted receiver is rendered anhydrous, and that when afterwards 

 exposed to a red heat a partial decomposition of the acid takes place ; 

 and this opinion he thinks strengthened by the consideration that 

 though no gas, nor anything but water, can be collected in converting 

 the phosphate into pyrophosphate, a peculiar bui-nt smell is given out; 

 and if the calcination of the salt (it having been previously dried gra- 

 dually) be effected in a glass tube, the salt may be observed to acquire 

 a carbonaceous tinge during the operation, which, however, vanishes 

 by a continuation or perhaps rather an increase of the heat. He 

 also adds, that though it has been asserted that a solution of the pyro- 

 salt becomes changed, by keeping, into the ordinary phosphate, such 

 has not been the case with a solution which he has kept from the 1 4th 

 December, 1835, till now, in order to prove the fact ; for it still conti- 

 nues to give a precipitate as perfectly white with nitrate of silver as it 

 did when newly prepared. 



Mr. Watson adds that there is a peculiar difference in appearance 

 between the calcined precipitate obtained from the pyrophosphate and 

 lime water, and the calcined precipitate obtained from the ordinary phos- 



voL. V. — 183G. E 



