83 JOURNAL OF THE 
tinues with greater rapidity the better the conditions, name- 
ly heat, which conditions prevailed in this case. 
The tallow used melted at 42° C. Normal tallow melts at 
from 43° to 46° C. The amount of lard present was there- 
fore comparatively small. The tallow was rancid, reacting 
acid with litmus paper. 
A chemical examination of the burnt portion showed the 
presence of nitric acid. This would have resulted from the 
decomposition of the dye which contains much nitrogen. 
Nitric acid was also detected in other portions of the material 
not charred, showing that the dye had been decomposed par- 
tially by the rancid fat, but not to such an extent as where 
the burning occurred. 
The dyeing was done in an alkaline bath (soda) to prevent 
this decomposition. The excess of this alkali is washed out 
and then the warp is sized. Rancid fat is acid and the acid- 
ity is increased by further oxidation of the fat, especially at 
the temperature named. This acid is liable to decompose the 
dye containing azo radicals liberating the oxides of nitro- 
gen, which tend to increase the oxidation. Experimental 
proof of this was obtained. The warps being confined in- 
stead of cooling nurse the heat until the temperature rises to 
the charring point of cotton. These conditions being allowed 
to continue fire would result, as happened in this instance. 
As stated above, while it is possible that gaseous coms= 
pounds capable of burning cotton could come from the dye, it 
is probably not the case here. Certainly there is no danger 
if the tallow is fresh. The fire therefore may be attributed 
to the spontaneous combustion produced by the continued 
oxidation of rancid tallow. The fact that it was rancid was 
evidence that the oxidation had begun. ‘Tallow that is only 
slightly rancid may be used with comparative safety when 
the process is rapidly carried out. The only absolutely safe 
plan however is to use fresh tallow. The rancidity of tallow 
shows itself by acid reaction to litmus paper, 
UNIVERSITY OF NorTH CAROLINA. 
