^3 C:ri^'!nimin and Graduation of BjVMt:'i Hydnmet.-r. 



Read of adopting the fimpler method of immediate numerical reference to the dcnfity of 

 water exprtflcd by unity, as is done in all modern tables of fpecific gravity, he had recourfe 

 to a proctfs fimilar to that of graduating the (lems of ihermometers from two fixed points. 

 The firft of thefe points' was obtained by immtrfing Iiis inftrument, which is the common 

 areometer, confiiling of a ball, (lem, and counterpoife, in pure water. At that point of the 

 flcm which was interfc£lcd by the furfacc of the fluid, he marked 2<-;o, or the commence- 

 ment of his graduations. In the next place he provided a number of folutions of pure dry 

 common fait in water : thefe folutions contained refpeclively one, two, three, four, &c. 

 pounds of the fait ; and in each folution the quantity of water was fueh, as to make up the 

 weight equal to one hundred pounds in the whole ; fo that in the folution containing one 

 pound of fait, there were ninety-nine pounds of water ; in the folution containing two 

 pounds of fait, there were ninety-eight pounds of water, and fo of the reft. The inftrument 

 was tlien plunged in the firft folution, in which of courfe it floated with a larger portion of 

 the ftem above the fluid, than when pure water was ufed. The fluid, by the intcrleclion of 

 its furface upc<i the ftem, indicated the place for marking his firft degree ; the fame ope- 

 ration repeated, with the fluid containing two pounds of fait, indicated the mark for tlie fe- 

 cond degree ; tlie folution of three pounds aflbrded the third degree ; and in this maimer 

 his enumeration was carried as far as fifteen degrees. The fiift fifteen degrees afterwards, 

 applied with the compaiTcs repeatedly along. the ftem, ferved to e.\tend the graduation as far 

 as eighty degrees, if required. 



This inftrument, which is applicable to the admeafurement of denfities exceeding that 

 of pure water, is commonly diltinguiftied by the name of the Hydrometer for falts. 



The Hydrometer for fpirits is conftruifled upon the fame principle ; but in this the 

 counterpoife is fo adjufted, tliat moft part of the ftem rifes above the fluid wlicn immerfed 

 in pure water, and tlie graduations to exprefs inferior denfities are continued upwards. A 

 folution of ten parts by weight of fait in ninety parts of pure water, affords the firft point, 

 or zero, upon the ftem ; and the mark indicated by pure water is called the tenth degree ; 

 whence, by equal divifions, the remaining degrees arc continued upwards upon the ftem as 

 far as the fiftieth degree. 



Thefe experiments, in both cafes, are made at the tenth degree of Reaumur, which anfwers 

 very nearly to fifty-five of Fahrenheit. 



M. Baume afRrms, that all his inftruments, conftrucled in thcfc methods, agreed together 

 with the utmoft precifion. From a few experiments, which however require to be care- 

 fully repeated, I am difpofed to apprehend tliat the folutions of common fait do not give a 

 fufiicicntly accurate original point, and that they may difl"er not only from the comparative 

 Jryntfs of the fait in difl^erent experiments, but likewife the ftate of its cryftals, whether 

 haftily or flowly feparated in their original fabrication, the purity being fuppofed the fame. 

 Such dilTerences muft confiderably affed the remote terms formed by repetition of the experi- 

 mental interval in either inftrument. I fuppofe all M. Baume's inftruments were conftrufled 

 from folutions made once for all, and referved for this purpofe; and that the French chemifts 

 who ufed them were fupplied under his direflion. For thefe reafons I am more inclined 

 to deduce the fpecific gravities from the experiments of himfelf and another accurate pof- 

 fcrfbr of thefe inftruments, than to recur to the original method of conftrudion. 



6 M. Baume, 



