This is not the place to follow the subsequent history of the Davy lamp, or to describe the various modifications which have grown out of it, or even to show the dangers which a larger experience reveals as latent in its original form. These dangers have in great measure arisen from the development of the very system of ventilation which Buddle himself instituted; and he who in his joy exultingly exclaimed, “At last, we have subdued this monster!” has unwittingly contributed to the maleficent activity of the monster in coping with the lamp as Buddle knew it.
In the course of his numerous trials made to elucidate the principle of the safety lamp, Davy observed certain peculiarities connected with flame which led him to take up the general question. Hence arose a series of investigations, which have contributed in no small degree to our knowledge of a particularly difficult and intricate subject.
He proved, in the first place, that flame must be considered as an explosive mixture of inflammable gas or vapour and air, and that the heat communicated by it must depend upon its mass. The different appearance of a flame of coal gas burning in a jet in the open air, and in his safety lamp mixed with common air, led him to investigate the cause of luminosity in flame. He says:—
“In reflecting on the circumstances of the two species of combustion I was led to imagine that the cause of the superiority of the light of the stream of coal gas might be owing to the decomposition of a part of the gas towards the interior of the flame, where the air was in smallest quantity, and the deposition of solid charcoal, which, first by its ignition, and afterwards by its combustion, increased in a high degree the intensity of the light.”
The principle of the increase of the brilliancy and density of flame by the production and ignition of solid matter explains the appearance of the different parts of the flames of burning bodies, and of the blow-pipe flame; it also explains the intensity of the light of those flames in which fixed solid matter is produced in combustion, e.g. phosphorus and zinc in oxygen, potassium in chlorine; and, on the other hand, the feebleness of the light of flames in which gaseous and volatile matter is alone produced, e.g. hydrogen in oxygen, phosphorus in chlorine. Davy’s theory has not been unchallenged, but all subsequent research, when pushed sufficiently far, has shown that, as regards all ordinary illuminating flames, i.e. carbonaceous flames—e.g. coal-gas, oil, paraffin, candle—the presence of solid incandescent carbon is a prime cause of their luminosity. It had been observed that the rarefaction of a mixture of inflammable gases diminishes its combustibility: Davy proved that this diminution was not the result of the removal of pressure per se, but of the cooling effect thus indirectly produced. Hence, the lower the temperature of ignition of a gaseous mixture the more it may be rarefied without becoming uninflammable. In like manner he shows that by heating the gaseous mixture it may be caused to explode at a lower temperature, and that when gases combine by sudden compression, the combination is caused by the heat evolved. Also that the power of an indifferent gas to prevent the explosion of a gaseous mixture depends upon its power of abstracting heat, and that the higher the temperature of ignition of the explosive mixture the less is the amount of indifferent gas required to stop the explosion. He proved that it was quite possible to effect the gradual combination of gases without flame—that is, without the production of heat sufficient to raise the products to incandescence; and he discovered the singular fact that platinum would induce the combination of many inflammable gases and vapours, and on this circumstance based the construction of his flameless lamp.
* * * * *
In the early summer of 1818, he thus wrote to his mother:—
“My dear Mother,—We are just going on a very interesting journey. I am first to visit the coal miners of Flanders, who have sent me a very kind letter of invitation and of thanks for saving their lives. We are then going to Austria, where I shall show Vienna to Lady Davy, and then visit the mines; and lastly, before I return, we are going to visit Naples.
“I have the commands of his Royal Highness the Prince Regent to make experiments upon some very interesting ancient manuscripts, which I hope to unfold. I had yesterday the honour of an audience from his Royal Highness, and he commissioned me to pursue this object in the most gracious and kind manner....
“We shall be absent some months. With kindest love to my sisters and my aunts,
“I am, my dear mother,
“Your most affectionate son,
“H. Davy.”
A few months after this visit to the Prince Regent he received the intimation that he had been created a baronet.
He arrived at Naples in the autumn, and began his researches on the Herculaneum manuscripts referred to in his letter. His first results were sufficiently encouraging to induce him to make some prolonged experiments with a view of discovering a method of unfolding them. He found that the papyri had suffered not so much from fire, as was believed, as from a gradual change in vegetable structure, similar to that which accompanies the transformation of vegetable matter into lignite. He managed to unroll a number, and an account of his results was communicated to the Royal Society in 1821. But from the fragmentary character of the papyri these were found to be of little value to literature. Subsequently difficulties were put in his way by the curators of the museum, and ultimately his investigations were abandoned, not without some little exhibition of temper and resentment on his part.