220 



Heat from in- 



combudible 



kodies. 



TWO NEW METAtS IN CRUDE PLATINA. 



lenticular or fpherical glafs, the rays are refrafled, and by 

 uniting in a focus, produce a heat capable of fetting fire to 

 the combuflible bodies within it. 



3. The Heat excited in Bodies not cotnhtjlihle. 



It is known that quick-lime plunged into water, or {imply 

 moiftened, produces a confiderable heat. This method has 

 even been employed with fuccefs for heating apartments, 

 green-houfes, hot-beds, i^c. at little expence. This property 

 of quick-lime of difengaging much heat by the contact of wa- 

 ter, and that, not lefs dangerous, of ditfolving or corroding 

 animal fubftances immerfed in it, require the greateft precau- 

 tions when a confiderable quantity of quick-lime is kept to- 

 gether. To preferve it, itmuft be protected from the conta6l 

 of the air and of every fpecies of humidity, and it muft be 

 carefully kept at a diftance from all combuflible bodies, fuch 

 as wood, hay, ftraw, S^c. which might inflame fpontaneoufly, 

 if the lime contradted the leaft humidity. The Journal de la 

 Haute-Saone gave an account, laft year, of the deftru6tion of 

 a barn, one of the wooden partitions of which took fire from 

 a heap of quick-lime, intended for the repairs of the farm, 

 having been carelefsly laid againfl it. 



In nature a great number of analogous phenomena occur, 

 in which bodies, by changing their compofition, or by con- 

 trafling new combinations, heat fo much, or difengage fuch 

 a quantity of caloric, that other combuflibles which are near 

 them may take fire. 



(To he continued.) 



XIX. 



New metal 

 Iridium, 



Difcovery of two nezv Melals in crude Flatina, By Smithson 

 Tennant, Ejq. F. R. S. 



jr\.T the laft meeting of (he Royal Society a paper of Mr. 

 Tennant was read, on the analyfisof the black powder which 

 remams after dilTolving platina, (hewing that it contains two 

 new melals, Mr. Tennant's firfl experiments were made hd 



fummer. 



