1 14 New Iii/trumerit for Mea/uring Specl/c Gravitiet. 



The method of fccurlng this inilrumcnt in its cafe will be better undeiilood from the 

 figure, tlun from the mod extended verb;)! defcription. 



Addition to the foregoing Memoir. 



THE conftant ufe I have made of the gravimeter fince I prefented the defcription to the 

 National Inltitute, has led me to make fome flight changes, by which its conftruflion is 

 rendered more eafy, and the effects of brittlenefs in one of its principal parts are removed. 



It has alfo appeared to be of fome utility to annex to this memoir the formula, by means- 

 of which, the gravimeter being once well adjulled, we are enabled, by a very fimple calcu- 

 lation, to find the fpecifc gravity of any fuhjlance whatever in proportion to that of dif.illcd 

 luater at the temperature of I 2. J degrees of the decimal thermometer, and 757-7 niiUimeters of 

 prejfure, -without the ufe either of difiilled luater, or the thermometer or barometer. The afto- 

 nifliment which I have fometimes remarked when the problem has been thus announced, 

 induces me to think that the folution here added will be acceptable, inltead of the reference 

 to the article Areometer of the Diftionary of Chemiftry, in the Encyclopedic Methodique. 



1 (hall likewife add an explanation of the figures which reprcfent the iuftrumcnt and 

 its cafe, together with examples of the application of tlie gravimeter to tables of fpecific 

 gravity. 



Defcription of a Solid Additional Piece for the Lower Bafon. 



THE condition of hermetically fealiiig the additional piece without changing its volume 

 neceffarily requires that the part near the aperture fliould be very thin. Hence it has fome- 

 times happened that the point was broken without any external blow, but merely in con- 

 fequence of the motion of the mercury contained within. A fimilar glafs bulb might in- 

 deed be added ; but this conftitutes but a fmall part of the remedy. For it is necefliiry to 

 adjull the inftrument again to preferve the property of meafuring the fpecific gravity of 

 the denfer fluids, and it has been found that this operation was not exempt from difficulties 

 when the defired degree of precifion was to be fought. 



I have remedied this inconvenience by fubftituting in the place of the glafs bulb loaded 

 with mercury a fmall mafs of folld glafs, as the (topper of a bottle, which is firft brought 

 to the proper form by grinding, and afterwards carefully diminifhed, until, when placed 

 m the lower bafon of the inftrument, its immerfion in diftilled water at the required de- 

 grees of temperature and prefliire (hall be exa(!!lly the fame as when the inftrument is 

 floated in the fame liquid with its eonftant additional weight in the upper bafon only. 



By this means there is a certainty of acquiring the utmoft degree of precifion at firft 

 trial ; becaufe the whole proctfs is reduced to the mere adjullment of a weight. 



Concerning the Application of the Gravimeter, to find the Specific Gravity of any Sitlfiance ivhiri- 

 tver, tvithout requiring Di/lilled Water, or the Thei mometcr or Barometer, or any fuhfequent 

 CorreiHen*. 



THE gravimeter being fuppofcd to be well regulated, let .v reprefent the fpecific gravity 

 fought J b the additional weight necelTary to fink the inflrument to the mark in the unknown 



fluid; 

 • There is a correflion overlooked by the celebrated author of this paper, and by almoU every writer otj 

 this fabjed. It arifes from the expanftoa or contra^on of the iollruincm itfclf, and of the folid under exa- 

 mination. 



