HYDRODYNAMICS. 



8. Formula tutted to the cote where the Gate* are perfectly saturated tvith Wakr. 



433 



In the following formultr, X is the weight of a volume of dry atmospherical air contained in the glass vessel, 

 at the temperature of 32, and the barometrical pressure of 0.76 metres or 29.99* English inches. 



T = the real tension of aqueous vapour at the weighing of the glass vessel empty. 



T' = the tension at the introduction of the gas. 



T"= the tension at the weighing of the glass vessel full of gas. 



X = 



P" P.0>.76 



(i +KO (p" |T") 



/ .0,00375 



1 + f .0,00375 



t" .0,00375 



* p^ O7fi - 



"_ P). .76 - 



Y = 



1 -f. I" .0,00375 



I + t .0,00375 



(No. 4.) 

 (No. 5.) 



T) 



1+f .0,00375 



These formula- win answer, when the external air, 

 in which the air and the gas are weighed, are not sa- 

 turated with moisture. In this case, T' and T" will 



ere at the time of the experiment, by the method 

 employed above, namely, by weighing a second time 

 the glass vessel empty, immediately after it has been 



express the tension of the aqueous vapour really sus- weighed full of the gas. Then, if I" is the tempera 



pended in this air. 



The preceding results may be rendered independent 

 of the quantity of aqueous vapour contained in the at- 



Y = 



ture at which this is done, p"' the atmospherical pres- 

 sure, T" the tension of the aqueous vapour, and 1' 

 the weight observed, the resulting formula will be 



I 



5X(1 + K/')T' 

 nno*T!r\ 



(No. 6.) 



(+''.o.' 

 (f T') 



- 0.00375) 



1 + f .0,00375 

 This formula become* exactly the same as No. 3, when T' = A; that is, when the gases are perfectly dry. 



3. Formula ndted to Ihe Cote mien the Catet are perfectly dry, but the exkatulion not complete. 



The above formula- will be sufficiently correct, if the exhaustion of the glass vessel is made with a very fine 

 w pomp ; but as this is not generally to be met with, let us suppose f to be the tension of the little air which 

 remains in the glass vessel, as marked by the gauge. Then 



(P'_P")0..76 + 

 / - fu t- 



Y = 



which, by the means formerly described, may be reduced to 



!'" .0,00375 



(Xo.7.) 





-. 0,00375)0*76 



Spreim 



M. Biot has exemplified the use of the formula No. 5. 

 by an experiment which he made on the 3d July 1806, 

 for the purpose of determining the specific gravity of 

 hydrogen gas. In this experiment, the different quan- 

 tities had the following value*. 



At the weighing of the emp- 

 ty glass vessel, 



At the introduction of the 

 gas into the glass vessel 



At the weighing of the glass 

 el when full 



U. fART f. 



P = 662.S6J grammes. 

 / = SO" 9 centigrade. 

 p =0.76 16 metres. 

 I" =21 4 centigrade. 

 = 0.7630 metres. 



p' = 

 P" = 



f =20*6 

 p" = 0.76*2 



The gas was saturated with water, and the hygro- 

 meter indicated a state of the atmosphere approaching 

 to extreme humidity. 



Weight of the atmospherical air 



atmosp 



in the glass vessel, as deter- 

 mined by preceding experi 

 menu 



;ix=7 



7.25S2 grammes. 



Log. X = 0.8605315 

 Cubical dilatation of glass for! 

 one degree of the centigrade V K = 0.0000262716 



3 i 



Log. K = 5.4194865 



