ON THE HEAT OF COMBINATION. 75 
violent action of nitric acid on zinc and copper, and the abundant evolution 
of gas which accompanies it. But the facility with which the gases may be 
condensed by the acid solution is probably not so generally known, and 
when the experiment is made for the first time cannot fail to excite surprise. 
If a small vessel of thin German glass, of about the capacity of half a fluid 
ounce, be half-filled with nitric acid of density 1:4, and a slip of zine be sus- 
pended in the upper part so as not to touch the acid, the flask hermetically 
sealed, and finally inverted while surrounded with cold water, a very violent 
action will occur, but without bursting the vessel. Having ascertained these 
facts, there was little difficulty in measuring the heat disengaged during the 
solution of the metals in nitric acid. The metal was weighed in a glass tube 
open at one end, which was introduced into a thin glass vessel containing 
nitric acid of specific gravity 1-4. The latter was then carefully closed and 
" introduced into a copper vessel filled with water, and suspended in a metallic © 

cylinder which was capable of rotation. On inverting the apparatus, the 
metal and acid came into contact, and the solution was completed in a few 
seconds. The rotation was afterwards continued for five minutes, which was 
sufficient to diffuse the heat disengaged through every part of the calorimeter. 
Solution of Zine in Nitric Acid. 
oF Hi ill. IV. 
Temperature ofair 4°5 6:2 8:0 58 
Increment found .. 2°66 2°78 2°83 271 
Increment corrected 2°65 2°77 2°82 2°71 
Weight of zinc .... O-587grm. O600grm. 0615 grm. 0°604 grm. 
Weight of water ..294°8 2844. 289'°3 2946 
Value of acid...... 7°4 69 65 66 
Value of vessels.... 14°3 14°3 143 143 
Heat of combination 1429 1411 1422 1420 
ne we have for the heat disengaged during the solution in nitric acid 
oI— 
; gg 0 wr ies pager 1420 
(Me = nL anal ll eae pa 5857 
Solution of Copper in Nitric Acid. 
“i I. ol ul ol: 
Temperature of air.. 8-9 6°8 7'8 8°5 
Increment found...... 2°56 2°58 2°58 2°57 
Increment corrected .. 2°55 2°56 2°57 2°56 
Weight of copper ....1°202grm. 1:204grm. 1-206 grm. 1:213grm. 
Weight of water.... 2'74*2 273°2 273°3 275°4: 
Value of acid ...... 14°5 168 15°6 15°5 
Value of vessels.... 16:8 16°8 16°8 16°8 
_ Heat of combination . . 648 652 651 650 
_ We have therefore for the heat disengaged during the solution in nitric 
acid of— 
L.SCM» COPPER os kryen de oso 650 
Li CGuhy. GODBCT ois 'zjerys ois: + 2578 
_ I made several attempts to determine the amount of heat disengaged in 
the solution of iron in nitric acid, but although acids of different strengths 
| were employed, I was unable to obtain satisfactory results, as the iron always 
assumed the passive state before a sufficient quantity was dissolved to raise 
the temperature of the water in the calorimeter through 1°. Silver, bismuth 
