ascertained that at first it gives out a pyrogenous acid, which occasions headache and tendency to sickness, and which is not a product of combustion at the moment, but exists ready formed; and that when charcoal is at a full red heat, this noxious substance is no longer given off.[1] Mr. Coathupe also thinks the cause of poisoning by charcoal fumes is an unknown pyrogenous body, and not carbonic acid gas.[2]—This department of inquiry is obviously susceptible of more precise information. But meanwhile, whatever may be the probability that, besides carbonic acid, some other gases, or some peculiar pyrogenous body, may occasionally exist in charcoal fumes, and increase their poisonous property, little doubt can exist that the carbonic acid is singly sufficient to account for all the leading phenomena.
M. Devergie has been led to the opinion that air, in which a fourth part of its oxygen has been converted into carbonic acid, and which therefore contains five per cent of that gas, is amply enough impregnated to occasion death.[3] This corresponds with the observations of M. Ollivier, who found that three per cent. was as much as could be breathed with impunity even for a moderate length of time.[4] Less, however, will suffice to prove injurious or even fatal, if the air be breathed long. Mr Coathupe inferred from a rough estimate, that in the dangerous experiment he made upon himself, the carbonic acid, if uniformly diffused in the apartment, which was probably the case, amounted to only two per cent.; but his data were inadequate.[5]
Proceeding from the fact that five per cent. of carbonic acid is sufficient to cause death, Devergie points out what quantity of charcoal is required to form that proportion,—a question of no small moment in respect to charges of murder, concealed under the semblance of suicide by suffocation with charcoal fumes. And he shows, that a French bushel, or decalitre, weighing 3000 grammes, is sufficient for a close apartment of 1275 cubic mètres, that is 6·6 pounds avoirdupois for a space of 1666 English cubic yards, provided the gas be uniformly diffused.[6] The quantity of charcoal burnt in a given case may be arrived at pretty nearly from the weight of ashes left, which is estimated in round numbers at a twenty-fifth by himself,[7] and at a twentieth by Ollivier.[8]
It is important to remark that complete closure of an apartment is by no means essential for the action of carbonic acid, whether disengaged within it or introduced from without. For poisoning has occurred, even where a window was partially open.[9]
3. It is probable that in some circumstances a very small quantity of the mixed gases proceeding from the slow combustion of tallow and other oily substances will produce dangerous symptoms. Dr. Blackadder remarked in the course of his experiments on flame, that the vapour into which oil is resolved, previous to its forming flame
