Mixture^ and its Effects. 101 



used to condense the vapour which is returned 

 back to the first vessel : this is called circulation. 

 In this process the condensing vessel is placed 

 above. Cohobation is an absurd term ; it, how- 

 ever, means the collecting of the vapour into 

 the second vessel, and pouring it back into the 

 first, as in circulation ; but instead of placing the 

 condensing vessel over the first, it is placed on 

 one side. 



By a knowledge of chemical attraction a che- 

 mist obtains the means of separating compound 

 bodies, viz. by applying "a third substance, in 

 order to decompound them b^ mta^o <*f tV,^ 

 superior elective attraction which one of the 

 bodies may have for that third substance. 

 Hence it appears that Sir Isaac Newton's 

 theory is extremely probable, yet it is not alto- 

 gether sufficient ; for why may not the three 

 substances unite ? This may perhaps arise from 

 a repulsion between the third substance and 

 one of the other two. But I am not inclined to 

 multiply causes. 



Geoffrey was the first who formed tables of 

 the elective attractions of bodies, which were 

 greatly extended and essentially corrected by 

 Bergman. 



The perfection of chemical science con- 

 sists in what is called chemical analysis, that 

 is, the resolving of bodies into their constituent 

 parts; and it is surprising to reflect how far 

 these operations have been carried by modern 



