Mr Clark on the Pyrophosphate of Soda, 303 



was let up to the top. The open end of the tube joined to 

 the little retort was introduced into this 

 jar so as to reach near the top, and to 

 terminate in the .1 inch of air. The 

 whole air including this .1 inch was not 

 more than half an inch. Heat was ap- 

 plied by means of a spirit-lamp, and it was intense enough to 

 melt the green glass. I earnestly watched for a gaseous pro- 

 duct ; but at the end of the experiment there was no increase, 

 save only .1 inch = .03 grain, if it were common air,, a quan- 

 tity so inconsiderable, that I conceived it to be of accidental 

 origin*, and inquired after it no farther. But there was ano- 

 ther product, which, considering the change that the salt was 

 undergoing, was hardly to be expected. In the narrow tube 

 there gathered small drops of a liquid, which, when examined 

 after the experiment, was found to be nothing else than wa- 

 ter, tasting a little burned indeed, but not affecting vegetable 

 colours. The salt which before being heated in the retort 

 gave a yellow precipitate with nitrate of silver, now gave a 

 white precipitate ; and a portion of it, being subjected to a 

 strong red heat in a platinum crucible, did not undergo the 

 slightest diminution in weight. 



The 23.45 grains of phosphate of soda dried on the sand- 

 bath lost 1.46 grains by the process in the retort. Now we 

 have before seen that 1. of crystallized phosphate of soda loses 

 .6167 of water by the sand bath, and leaves .3833. But 

 23.45 : .3833 : : 1.46 :..0245. Hence the result of the experi- 

 ment may be stated : 



Dry pyrophosphate of soda, - 21 .99 .3588^ 



Water, expelled by a red heat, - , 1 .46 .0245 



23.45 .3833 



• The small retort and its contents being weighecj, the tube was adapt- 

 ed to it and cemented in the evening, and the experiment described in the 

 text tried next morning. As the salt in the small retort was in a porous 

 state, I think it not improbable that, like other porous substances, it may, 

 in this interval, have absorbed air to the extent of .1 inch. This absorp- 

 tion would not affect the weights taken in the experiment, as the weighings 

 were both made before the substances had more than time to cool, after 

 removal from the sand-bath, and from the fire. 



