PHYSICAL AND LITERARY. 27 



£»f Experirnent 3, 6. 7. the proportion of 

 this earth was confiderahly greater than - 

 ju the marles of Experiment 10. 11.; yet, 

 ^fter fufficient burning, the latter relent- 

 4sd in water, the former not. Nay, when 

 a part of a bed of ftone, which contained 

 only one third of calcarious earth, was 

 -calcined and put into water, it inftanrly 

 fell down into powder j whereas marie, 

 containing four fifths of calcarious earth, 

 underwent no fuch change from the fam? 

 Itreatment. 



Th E caufe of the difference then muQ: 

 be fought for in the unfbluble part ot 

 thefe fubflances. Upon comparing the 

 Experiments related in Sedions 5. and 6. 

 I obferve, that all the reftdua, coiiGiliag 

 of any confiderable proportion of idnd, 

 were extracted from fubiUnccs which, in 

 a natural ftate^ fufFered very little change 

 from water ; tho', after calcination, water 

 immediately reduced them to powder. 

 On the contrary, the refidiia of clay werq 

 obtained froni bodies poiTeffed of ju(l thq 

 oppoiite properties. That thii, obferva- 

 tion wjU apply iiniverfally, I dc^renot ven- 

 ture 



