DESCRIPTION OF AN HYDROMETER. 51 



The other alteration, though it will be highly acceptable to Hydrometer 

 fchilofophical men, and renders the inftrument of more exten- ^J|^ ^^1 

 five utility, and independent of the Aiding rule, feems not fo ated on its ftem. 

 clearly to be an amelioration with regard to its moft frequent 

 and daily ufe. Inftead of the letters of the alphabet, the four 

 faces of the ftem carry graduations which at once point out the 

 fpecific gravity of the fluid according to the form now univer- 

 fally adopted ; namely, by taking water as unity. Its figure 

 is fliownin Plate IV. Fig. 1. and it is provided with three 

 weights ; the inftrument itfelf being ufed without a weight at 

 the upper range of denfities. 



Upon this occafion I cannot avoid noticing the ftrange over- Remarkable 

 fight of philofophers and others, who have exprefled the den " ^hkal^he- 1 " 

 fities of acids and other fluids by certain graduations or degrees m ift s in noting 

 of inftruments, fuch as that of Baum^ and others; the com-{pe c jfi c J ravitie » 

 parative values of which were either little known to the pub- f f ome part i C u- 

 lic, or ill determined ; fo that a very eflential part of what we lar inftrument. 

 read in books of chemiftry is to many readers void of meaning. 

 This is the more remarkable, fince the expreffion of fpecific 

 gravities before mentioned has been long eftabliftied, and is 

 quite as eafy to be put upon an inftrument as any other nota- 

 tion. It is now feven years fince I urged this matter in my Long ago no- 

 chemical dictionary at the article Hydrometer, and the evil u " d b y thc au " 

 ftill remains. If my recollection be accurate, I think Briflbn and by Briflwu 

 made the fame propofal many years ago in the Memoirs of the 

 French Academy. In the prefent inftance, Mr. Atkins gains Advantages in 

 the advantage of Amplifying his Aiding rule by leaving out the Jjjjr^ jjjjj! At ~ 

 alphabet, fo that the operator looks for the fpecific gravity in rule 5 

 the firft inftance, and upon the oppofite lines he finds the 

 itrength and concentration. 



But ftill more it is worthy of notice, that if he poflefTed the and rendering 

 inftrument only, or ftiould in preference be defirous of r efer- the ^"ableTo "u 

 ring to Gilpin's tables, or any other elementary courfe of ex- tables, &c. 

 periments, he can proceed immediately from the inftrument to 

 the table without ufing the Aiding rule to determine his fpecific 

 gravity, as he muft with the other. 



I was at firft very ftrongly impreffed with the facility of this 

 inftrument in giving a refult which ordinarily demands to be 

 computed, and I fuppofe the advantages above ftated will fe- 

 cure it the preference with many. But upon reflection, I But the alpha- 

 cannot but think the alphabetic inftrument intitled to the pre- app€ ^ better" 

 E 2 ference adapted for dif- 



