390 Scientific Proceedings, Royal Dublin Society. 



The following is a very convenient modification of our 

 formulae which is applicable to all such cases : — 



G 2 r 0,1 D l X, 



K L" * J " E " 12' {3) 



where 



(t 2 is the weight in grammes of the reagent, 



Gi the weight of the gas evolved, 

 2? 2 the bond- weight of the reagent as defined below, 1 

 B x the bond- weight 2 of the gas evolved, 

 D y its density 2 compared with hydrogen, 

 and Li the number of litres evolved. 



This formula will find L x when G 2 is given, and G % when L x is 

 given : i. e. it will find either the volume of gas which a given 

 weight of the reagent willf urnish, or the weight which is consumed 

 in disengaging a given volume of gas, all at standard pressure 

 and 21° temperature. 



To the result so obtained the corrections for temperature and pres- 

 sure given on p. 387 may be applied. 



In the present case we are to make L x equal to 7, and we 

 know that D x is 1 ; B x is 1 ; and B 2 is 321. Introducing these 

 numbers we find 



G 2 = 321 x _2_ = 19 } very nearly. 



This accordingly is the number of grammes of zinc that would 

 evolve 7 litres of the gas at the temperature of 21° and at standard 

 pressure. 



To get the result at 15° of temperature, and under 31" of 

 pressure, we have to correct for 6° deviation in temperature, and 1" 

 deviation in pressure. Now we found above that the 



temperature correction for 6° = 2 per cent., 

 barometric correction for V = 3^ per cent. 



1 The bond- weight means the part of the atomic weight to be allotted to each bond 

 engaged in the reaction. Thus, the bond-weight of His 1, and the bond weight of Zn 

 is half its atomic weight, since there are two bonds of zinc engaged in the reaction 

 that occurs in this case. 



2 I)\ and i?i are usually the same number. 



