CHEMISTRY: RICHARDS AND DAVIS 
53 
dipping into the substance to be ignited first, whether this was sugar, 
napthaJene or parafhn. A current of approximately 0.8 ampere ig- 
nited the cotton wool in about one-fifth of a second. The variations 
in the amount of heat ob tamed from the current in this time are wholly 
negligible in results like these, where one substance is measured by com- 
parison with another treated 
in the same way. 
The automatic control of the 
temperature of the environ- 
ment. — In a recent commu- 
nication from this labora- 
tory an automatic device, or !^ 
'syn thermal regulator/ for 
causing the environment 
around the calorimeter to 
match the temperature of 
the calorimeter itself, is de- 
scribed.^ The present inves- 
tigation was well in progress 
before this synthermal regu- 
lator was perfected, and in 
the meantime we had 
evolved a quite different 
much simpler device which 
served the present purpose 
sufficiently well, although 
not so generally useful as 
the other. 
The general impression 
seems to exist that combus- 
tion within the calorimetric 
bomb is explosive and instan- 
taneous.^ According to our 
experience, this is by no means the case, especially with solid substances. 
We find that the rate of combustion is very variable, depending partly 
upon the nature of the substance, partly upon the state of aggrega- 
tion, and partly upon the oxygen pressure. Thus benzoic acid or naptha- 
lene in powder, or a volatile liquid cause the temperature of the calori- 
metric system to rise very quickly when they are burned; but if the solids 
are compressed into hard tablets, the temperature rise is slow and 
steady and may require over three minutes for completion. The dif- 
/o 20 
H'me /n seconc/s 
FIG. 2 
Continuous lines A and B represent temperatures 
in calorimeter as indicated by thermometer in com- 
bustions of two different speeds. 
Broken lines C and B indicate rise of temperature 
in environment as produced by apparatus to be de- 
scribed and illustrated in figure 3. 
