BY COMiPRESSIONo 405 



the fourth experiment was made on the 2d of May, like Fourth experi- 

 U.c reft in all refpeas, with a ftill fmaller air-tube, of 0.0318, ^^eater "pteffare, 

 being lefs than one thirtieth of a cubic inch. The upper py- fufion at a mu- 

 rometer gave 2,)°, and the under one 16* : The loweft malTes fl^gJt^iJ^'oV 

 of carbonate were fcarcely affeded by the heat. The contents carbonic acid, 

 of the little tube loft 2.9 per cent, bolh the lump and the ^'*^' 

 pounded chalk were in a fine faline ftate, and, in feveral places, 

 had run and fpread upon the infide of the tube, which I had 

 not expected to fee in fuch a low heat. On the upper furface 

 of the chalk rammed into the little lube, which, after Its in- 

 troduction had been wiped fmooth, were a fet of white cryf- 

 tals, with thining facettes, large enough to be diftinguithed by 

 the naked eye, and feeming to rife out of the mafs of car- 

 bonate. I Ijkewife obferved, that the folid mafs on which 

 thefe cryftalyftood, was uncommonly tranfparent. 



In thefe four experiments, the bulk of the included air was Obfervations -. 



fucceffivfly diminlftied, and by that means its elafticity in-- !j^^J"J°^Jg'J''=* 



creafed. Tiie confequence was, that in the firft experiment, beats when the 



where that elafticity was the leaft, the carbonic acid vvas'^!<=^P^.f\ *^^''°' 



. nic acid is pre- 



allowed to feparate from the lime, in an early ftage of the vested. The 



nfing heat, lower than the f'ufing point of the carbonate, and ^<*"^ ^^^ " * 

 complete internal calcination was effe6led. In the febond 

 experiment, the elaftic force being much greater, calcina- 

 tion was prevented, till the heat rofe fo high as to occafion 

 the entire fufion of the carbonate, and its a6lion on the tube, 

 before the carbonic acid was fet at liberty by the failure of 

 the barrel. In the third experiment, with ftill greater elaftic 

 force, the carbonate was partly calcined, and its fufion 

 accompliftied, in a heat between 41** and \5'^. In the hit 

 experiment, where the force was ftrongeft of all, the carbon- 

 ate was almoft completely protcfled from decompofition by- 

 heat. In confequence of which it cryftallized and adted on the 

 tube, in a temperature between 25° and 16*. On the other 

 hand, the efficacy of the carbonic acid as a flux on the lime, 

 and in enabling the carbonate to aft as a flux on other bodies, 

 was clearly evinced; fince the firft experiment proved that 

 quicklime by itfelf could neither be melted, nbr ai^t upon porce- 

 lain, even in the violent heat of 79* ; whereas, in the laft 

 experiment where the tarbonic acid was retained, both of 

 Ihefe efife^s took place in a very low temperature, 

 (To be continued, J 

 Vol. XIII. — SvPi-LKMEFT. Ff IV, Qb/ervatwtt^ 



