442 New Experiments on some of 
tion, and satisfied myself that it was the same as that formed by 
other methods, it became evident that there were no sources of 
error in the experiments on the combustion of phosphorus in oxy- 
gen gas, arising from the formation or separation of water; and 
the only circumstance which could be urged against the accuracy 
of processes on this combustion, was the small quantity of ma- 
terials * on which they had beeu made. 
The vividness and rapidity of the combustion of phosphorus, 
renders it impossible to burn considerable quantities of phos- 
phorus in the common way in glass vessels. Phosphuret of lime 
burns much more slowly and Jess intensely. I endeavoured to 
ascertain the quantity of oxygen absorbed by a given weight of 
phosphorus converted into phosphuret of lime; but the experi- 
ment did not succeed. Though the phosphuret of lime was in 
fine powder and distributed over a large surface, yet the phos- 
phate of lime which formed and fused on the exterior, defended 
the interior of the phosphuret from the action of the oxygen, and 
prevented its combustion. 
After various unsuccessful trials to convert considerable quan- 
tities of phosphorus into phosphoric acid by combinations con- 
taining oxygen, | at last thought of a verysimple mode of burn- 
ing phosphorus, which answered perfectly. 
Phosphorus requires a considerable heat for its volatilization. 
By inclosing it in a small tube, so constructed that the phos- 
phorus cau burn in vapour only from the aperture of the tube, 
large quantities of it may be burnt by the heat of a spirit-lamp 
in a retort filled with oxygen, and the absorption of oxygen and 
the quantity of phosphoric acid formed may be minutely ascer- 
tained. 
The accompanying sketch (PI. V. fig. 1.) will give an idea of 
the apparatus. The neck of the little curved tube, or small distill- 
ing retort, after the phosphorus is introduced, is drawn out, and 
an aperture left of about1-10th of an inch; it should not be smaller, 
or it becomes choked by the phosphoric acid formed. Regu- 
lating the heat by raising or lowering the spirit-lamp, the com- 
bustion may be carried on slowly, or rapidly, at pleasure. 
Operating in this way, I have often burnt from 5 to 10 grains 
of phosphorus withous any accident, and ascertained exactly the 
quantity of oxygen absorbed : -there is only one source of error 
—a quantity of phosphorus remains in the upper part of the tube, 
which cannot be burnt except by a greater heat than the retort 
* A source of error might be suspected in carbon combined with phos- 
phorus ; but I have been convinced by experiments made on the action of 
chlorine on the phosphorus I employed, that it contained no appreciable 
quantity of carbon. I suspect that what is o'ten taken for carburet of phos- 
phorus, is in reality a red oxide. 
will 
