2i8 ESSAYS AND OBSERVATIONS'. 



That the fixed alkali, in its ordinary ftate, 

 is feldom entirely faturated with air, feems to 

 be confirmed by the following experiment. 



I expo fed a fmall quantity of a pure vege- 

 table fixed alkali to the air, in a broad and 

 fhallow vefTel, for the fpace of two months ; 

 after which I found a number of folid 

 cryftals, which refembled a neutral fait fo 

 much as to retain their form pretty well in 

 the air, and to produce a confiderable degree 

 of cold when diflblved in water. Their tafte 

 was much milder than that of ordinary fait 

 of tartar i and yet they feemed to be com- 

 pofed only of the alkali, and of a larger 

 quantity of air than is ufually contained in 

 that fait, and which had been attraded from 

 the atmofphere : for they ftill joined very 

 readily with any acid, but with a more vio- 

 lent effervefcence than ordinary; and they 

 could not be mixed with the fmalleft portion 

 of vinegar, or of the fedative fait, without e- 

 mitting a fenfible quantity of air. 



As it now appeared that feveral alkaline 

 fubftances have an attraction for fixed air, I 

 tried a few experiments to learn the relative 

 ftrength of their feveral attractions. ■ 



Twenty 



