NEW FORM OF CALORIMETER. T49 
found to be thermally equivalent to the apparatus is added to 
the quantity of water actually used. The specific heat of. this 
amount of water, compared with the rise in temperature as above 
determined, gives the actual number of calories of heat con- 
tributed to water and apparatus by the combustion. The total 
heat thus contributed includes the heat of combustion of the 
substance itself plus the heat of oxidation of the iron wire and 
the heat of formation of a certain amount of nitric acid, which is 
at the same time produced in small but varying quantity. To 
determine the heat of oxidation of the iron each wire is weighed 
at the outset, When, as is sometimes the case, a portion is left 
unoxidized, this is weighed at the end and the difference is taken 
as the amount oxidized. The purest piano wire is used and the 
heat produced is estimated from the amount oxidized and the oth- 
erwise observed heat of oxidation of iron (for Fe, O, 1,600 small 
calories per gram of Fe). ‘The nitric acid which is dissolved in 
the water formed by the combustion in the bomb is rinsed out 
and the amount is determined by titration with a standard solu- 
tion of sodium carbonate, one cubic centimeter of which will 
‘neutralize a quantity of nitric acid of which the heat of formation 
is one small calorie. Adding the heats due to the oxidation of 
the iron and the formation of nitric acid and subtracting the 
sum from the total heat communicated to the apparatus and 
water leaves the amount due to the oxidation of the substance. 
There are, of course, numerous details of manipulation sug- 
gested by experience which hardly need be described here. One 
for instance is the use of a kindling material for animal and 
vegetable fats, in which the molten globule of iron oxide some- 
times sinks until it is covered without igniting the substance. 
By laying a small portion, three to five milligrams, of naphtha- 
lene on top of the substance, ignition is made sure. Allowance 
is made for the heat of combustion of the naphthalene, which, 
for that we have used, is found to be 9,678 small calories per 
gram. 
One essential feature is the oxygen. This we formerly obtained 
from Berlin, but it can now be had in New York, of satisfactory 
purity, in cylinders ready for use. With only a single cylinder, 
a force pump would be necessary to charge the bomb as soon as 
the pressure in the cylinder should fall below 20 atmospheres, 
which is the pressure required in the bomb. To avoid the 
necessity of a force pump we employ two cylinders with a device 
