300 Experiments and Jnferenus refpeHlng 



having been announced by Landriani. To determine whether the aggregation of. the ftone 

 were the caufe of ihs, another diamond was fubjecSed to experiment, fcarcely exceeding the 

 . eighteenth part of die former; but this gave no fign of inflammation, nor underwent the leaft 

 cliange. 



(-^n the 23d the diamonds were taken out and carefully examined, when the larger was 

 found to have loft 54 milligrdmrnes, or o, j8 of its weight, having preferved its original form, 

 though the angles were blunted, and its furface tarrliflied arid full of fmall inequaliti s, which 

 under the magnifier prefented either pointed projections, or the feiSlions of parallel plates. In 

 feveral of the cavities were feen a greyifli kind of fpot ; and, in particular, in a cavity IbmC' 

 what larger than the reft, where the focal fpot appears to have been moft ftrongly aftive, 

 there was a blackilh ftreak not terminated, as if drawn externally, but fufed, and penetrating 

 by a degradation of colour into the body of the ftone. 



This diamond was preferved for infpeftion, and another of a clearer water than the former, 

 of an octahedral form, and the weight of 200,1 milligrammes, was expofed to the focus of 

 the great lens of Tfchirnhaufen, which is 32 French inches in diameter, and 73 inches in its 

 focfal length: but the focal length was fhortened by the interpofition of another lens. The 

 firft experiment fcarcely exhibited any figns of combuftion, and failed by the breaking of the 

 receiver. In the following year, 6, it was therefore found expedient to refume the procefs 

 with a large -lobe, in order that its furface might be at a fuificient diftance from the denfer 

 part of t'.e luminous cave. The globe made ufe of meafured 28,63 centimetres in diameter, 

 and its capacity was 12325 cubic centimetres ; and, in order to determine the quantity of 

 fpace occupied by the rifing mercury, there was a piece of paper pafted on the outfide, hav- , 

 ing marks thereon to exprefs every J 00 cubic centimetres, determined by pouring in water 

 by a meafure of th. t magnitude. 



As it was imprafticahle to exclude the air from fo large a veflel of glafs, by means of the 

 vaft quantity of mercury it could contain, our operators had recotn-fe to an ingenious expedient 

 derived from the confideration that the fpecific gravity of oxygen gas is about one ninth part 

 greater than that of common atmofpheric air. It confifted in admitting the gas by a tube 

 which reached from the neck (then turned upwards) to the lower part of the infide, while 

 the common air was fuffered to efcape through another fhort tube in the cemented cork by 

 which the orifice was clofed. It may eafily be imagined, that the oxygen did not difplace the 

 common air without mixing with it and becoming more or lefs contaminated with azote; for 

 which reafon it was neceflary that the contents fhould be thus difplaced for feveral fuccelHve 

 times. By this treatment the laft portions of gas extruded were found to be pure, and the 

 veflel continued perfedlly clean and dry. The authors give a de^il of the methods by which 

 the oxygen gas was obtained, and its purity afcertained. 



Fig. 2 reprefents the globular veffel inverted over an iron mortar, containing mercury, and 

 fecured in its place between two pieces of wood, which formed a cavity to receive it. The 

 diamond was previoufly fecured in a fmall veflel of baked clay, by means of a ribband, which 

 was afterwards flipped off when the veflfel was inverted. There was a fmall tube of commu- 



ntcatioB 



