ON GASEOUS EXPLOSIONS. 255 
Such a motor on account of its high speed is well suited for the investiga- 
tion of this question; in some of Dr. Watson’s experiments as little as 
3p Of a second elapsed between the ignition of the mixture of petrol and 
air and the discharge of exhaust gases. The most important part of 
Watson’s work from the point of view of the Committee is the simul- 
taneous measurement which he has made of the quantities of air and of 
petrol taken into the engine and of the chemical composition of the 
exhaust gases. 
Several observers have found that even when the combustion in the 
petrol engine is apparently perfect, there being some excess of oxygen 
and no carbon monoxide or hydrogen in the exhaust, the ratio of hydro- 
gen to carbon in the exhaust gases is considerably greater than in 
the petrol used, showing that even in this case there must be some in- 
complete combustion.’ The very complete set of analyses taken by Dr. 
Watson, of which he was good enough to give full particulars to the 
Committee in Note No. 7, before his paper was published, bear out this 
observation, and show that the discrepancy between the composition of 
the exhaust gases determined in this way and that of the petrol is not 
due to errors of experiment. 
Some evidence as to the cause of the discrepancy is furnished by 
some experiments of Hopkinson, who found that by exploding the 
residue of the exhaust, after absorbing CO and H, with electrolytic gas 
a considerable further yield of Co:, amounting to nearly 5 per cent., was 
obtained. Hopkinson also found that the residual combustible gas re- 
vealed in this way was soluble in water, which points to the possibility 
that it may be an aldehyde or possibly acetylene. It is known that in 
the combustion of hydrocarbons, such as petrol, with insufficient 
oxygen, considerable quantities of aldehyde are formed, but so far as 
the Committee are aware the question has not been fully investigated 
where sufficient oxygen is present to burn the petrol. It is at least 
possible that the effect may be due to deficient vaporisation or incomplete 
mixture in the combustion as it occurs in the petrol motor, and that it 
would not happen if the petrol were completely converted into vapour, 
_ and that vapour sufficiently intimately mixed with the air before combus- 
tion took place. Prof. Bone, however, considers that the combustion of 
a hydrocarbon with insufficient oxygen is not different as to chemical 
actions from combustion with excess oxygen, and he dissents from the 
view that the effect observed may be due to deficient vaporisation or in- 
complete mixture. The question is one well worthy of the attention of 
those chemists who are engaged in the study of the combustion of 
hydrocarbons. Whatever the explanation, the practical result esta- 
blished by these experiments of Watson and Hopkinson is that the petrol 
is rarely, if ever, completely burnt in a motor fed by the ordinary types 
_ of carburettor, even when there is apparently a considerable excess of 
oxygen. 
Neither Waison’s nor Hopkinson’s experiments, which are in full 
agreement with one another, suggest that the incomplete combustion 
occurring in the petrol motor is conditioned in any way by the speed of 
revolution. It is probable, therefore, that it is not incomplete combus- 
tion of the kind contemplated by the Committee and referred to in their 
* Hopkinson, Engineering, August 9, 1907; Clerk, Proc. Inst. Auto. Enq., 
December 1907; Hopkinson, Proc. Inst. Auto. Eng., February 1909. 
