ATWATER'S CALORIMETER. 7 l 



reduces to the determination of a maximum and to one multi- 

 plication if we have 



a(P+P) = o.2V+i.6p' (3) 



Now from the tests made we readily see that whatever 

 value a may take, it increases with the quantity of heat gen- 

 erated in the bomb | it is a little greater when the external air 

 is warmer than when it is cooler a fact which may be attrib- 

 uted to the influence of evaporation on the cooling of the 

 bath.* 



On the other hand, the nitric acid appears to increase with 

 the quantity of heat generated, and tends to offset the cor- 

 rection from a. In short, p' is, within certain limits, at the 

 control of the observer, same as P '. We consider it then 

 possible to arrange once for all so as to have the expression 

 (3) sufficiently close for industrial purposes. 



This can be done with Mahler's apparatus. Thus for oil 

 of colza the multiplication A(P -\- P} gave 9625 calories, 

 which is within ^-gVo ^ ^ e ^ na ^ num ber obtained after all 

 corrections; with the Nixon's coal we found t iat A(P-\- P') = 

 8418 calories, which differed ^- from the correct number; 

 with coal-gas the product 2681 X 1.28 = 3432 calories, while 

 the corrected result was 3418, or -yfa difference. 



ATWATER'S CALORIMETER. 



Prof. Atwater has considerably modified the bomb, so 

 that it seems to have some advantages for easy working. 

 Fig- 2 5 gives a sectional view of it in the calorimeter. The 

 steel used is the same as that used in the Hotchkiss guns, 



* The rapidity of cooling in the apparatus employed by Mahler was, 

 according to experiments, between 15 and 20 C. 



dB 



= o.oos(r- 7 1 .), 



To being the temperature at which cooling ceases. 



