t7}e Comhujl'ion af^fx i)tamon^ 299- 



tfolrved' tu^e. On the other fide was a pneumatic trough C, containrng water, in whicR witS - 

 a large pneumatic veflel D, communicating with the interior of A, by means of a tube pro- 

 perly Bended. The corhmunfcation could be regulated at pleafure by the cock E. On onfo~ 

 fide of the trough of mercury was a bar F F, to which a clamp G could be fixed at plea- 

 fure; and through the upper part of this clamp was pafled a rod of hard wood H, which- 

 pafled beneath the mercury, and icffe again fo afford a fupport for the diamond at I. By aH- 

 tering the fituation of the cFamp G, by elevating or" deprefli'ng the rod H, or By turning this.- 

 laft on its axis, it was poflible to place the extremity I in any requiretl fituation within tfic 

 glafs veflcf A. At I ^^.s placed a fiiiall porcelain crucible, in which the diamond was 

 placed. This crucible was pro^i<fed withaftogpery which could ba put in and out by":- 

 ftifeans' of a wire. 



The diamond which was the fubjeft of this experifnerit was an incomplete aSlahedron, of"a 

 dull water, inclining to yellowifli-grey, fomew'hat rounded on the edges. It weighed exa£tl)r« 

 142 milfigrammes. In this fituation of the apparafuSj the crucible being clbfed'," the pum^ 

 ■p^as worked umtil the mercury rofe to within le(s than one millimetre from the orifices of the 

 communicating tubes, wliich terrriinated quite at the upper part of" the vefT;! at A. The 

 tock E was then opened, and oxygen gas, obtained from the oxygenated muriate of potafli, •■ 

 and previoufly piit into D, was paffed into A. The firft portions of this gas which mixed with - 

 the minute refidiie of common air at A, were drawn off by the air-pump, in order to exhauft 

 fhe common air as much as pofilbte; and at laft the veffcl A was filled with the oxygen gas*, - 

 which might be confidered as nearly ptire. 



The folar Keat was applied to the diamond liy means of the great lens belonging to the Poly"- 

 fecKhic fchool, the diameter of which is 40,59 centimetres, and its focus I35v3. The effeft of 

 the fudden heat upon the glafs veffel was moderated by occafionally intercepting the rays with- 

 p'aper for a few inftants, after which the diiniond being eXppfe'd to the focus for twenty mi- - 

 ttutes did not take fire. It appeared at fii-ft farinaceous, and afterwards perceptibly blackened- 

 on its fiirface, when examined through coloured glailes, while the focus was upon it. When * 

 fhe focus wa< intercepted by an opaque body, in order to examine the diamond rnore accurately, 

 the diamond appeared tb have undergone no alteration but that of having acquired a yellowifli ^ 

 fliade, peffe^ly refembling cftar amber.- At this period the experiment Was difc'bntinued,'oti> 

 afccount of the weather becoming obfcure. 



On the following day the folar f6cus was thrown upon" the diamond, and at the ertdbf orfc" 

 hour and fourteen minutes, the corie of light being intercepted, the diamond was feen dif- • 

 ti'niSIy ; tr'anfparent afiid' fiirrounded' by a weak radiation. When it was cold its edges •• 

 appeared t6 haVe been fbftened^' A' black point wasvifible ; but the diamond had recovered ^ 

 its white colour by the lofs of the yellow tinge it-had acquired 'the day before. • 



Th'6 experiment could not tfS refumed till the 15th. On this day the weather was imfaVour- - 

 rfjjfe, but rievertheiefs a ffight fCintillation appeared. — To the aftbnifhment of the operators, the 

 diamond did not continue its own combuftfon, which' even metallic fiibftances do when fu?- 

 ficiently heated- in oxygen gas; Thif feemed the more remarkable on account of the contrary - 



hftvini 



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