LAVOISIER ADDRESSING A GROUP OF SCIENTISTS

(From a panel by Barrias on the Lavoisier Memorial, Place de la Madeleine, Paris)

the result of the combination of the elastic fluid set free from the metal and that set free from the charcoal; thus, though this fluid is obtained in the state of fixed air it is not justifiable to conclude that it existed in this state in the metallic calx before its combination with the carbon.

These reflections made me feel how essential it was--in order to unravel the mystery of the reduction of metallic calces -to perform all my experiments on calces which can be reduced without addition of charcoal....

Precipitated mercury, which is nothing else than a calx of mercury, as several authors have suggested and as this memoir will further show, precipitated mercury, I repeat, seemed to me suitable for the object I had in view: for nobody to-day is unaware that this substance can be reduced without addition of charcoal at a very moderate degree of heat. Although I have repeated many times the experiments I am going to quote, I have not thought it suitable to give particular details of any of them here, for fear of occupying too much space, and I have therefore combined into one account the observations made during several repetitions of the same experiment.

In order to be sure that precipitated mercury was a true metallic calx, that it gave the usual results and the usual kind of air on reduction by the ordinary method, that is to say, using the recognized expression, by the addition of phlogiston, I mixed one ounce of this calx with 48 grains of powdered charcoal, and introduced the whole into a little glass retort of at most two cubic inches capacity, which I placed in a reverberatory furnace of proportionate size. The neck of this retort was about a foot long, and three to four lines in diameter; it had been bent in a flame in different places and its tip was such that it could be fixed under a bell-jar of sufficient size, filled with water, and turned upside down in a trough of water....

As soon as a flame was applied to the retort and the heat had begun to take effect, the ordinary air contained in the retort expanded, and a small quantity passed into the bell-jar; but in view of the small size of the part of the retort. that remained empty, this air could not introduce a sensible error, and at the most it could scarcely amount to a cubic inch. When the retort began to get hotter, air was very rapidly evolved and bubbled

up through the water into the bell-jar; the operation did not last more than three-quarters of an hour, the flame being used sparingly during this interval. When the calx of mercury was reduced and air was no longer evolved, I marked the height at which the water stood in the bell-jar and found that the air set free amounted to 64 cubic inches, without allowing for the volume necessarily dissolved in the water.

I submitted this air to a large number of tests, which I will not describe in detail, and found (1) that it combined with water on shaking and gave to it all the properties of acidulated, gaseous, or aerated waters such as those of Seltz, Bougues, Bussang, Pyrmont, etc.; (2) that animals placed in it died in a few seconds; (3) that candles and all burning bodies were instantly extinguished therein; (4) that it precipitated lime water; (5) that it combined very easily with fixed or volatile alkalis, removing their causticity and giving them the power of crystallizing. All these are precisely the qualities of the kind of air known as fixed air, such as I obtained by the reduction of minium by powdered charcoal, such as is set free from calcareous earths and effervescent alkalis by their combination with acids, or from fermenting vegetable matters, etc. It was thus certain that precipitated mercury gave the same products as other metallic calces on reduction in the presence of phlogiston and that it could consequently be included in the general category of metallic calces.

It remained to examine this calx alone, to reduce it without addition, to see if some elastic fluid was still set free, and if so, to determine the nature of such fluid. With this in view, I put into a retort of the same size as before (two cubic inches) one ounce of precipitated mercury alone; I arranged the apparatus in the same way as for the preceding experiment, so that all the circumstances were exactly the same; the reduction was a little harder to bring about than when charcoal was present; it required more heat and there was no perceptible effect till the retort began to get slightly red-hot; then air was set free little by little, and passed into the bell-jar, and by keeping up the same degree of heat for 2 hours, all the mercury was reduced.

The operation completed, I found 7 gros, 18 grains of liquid

mercury, some in the neck of the retort and some in a glass vessel I had placed at the tip of the retort under the water; the amount of air in the bell-jar was found to be 78 cubic inches; from this it follows, if the loss of weight of the mercury is attributed to the loss of this air, that each cubic inch must weigh a little less than two-thirds of a grain, which does not differ much from the weight of ordinary air.

Having established these results, I hastened to submit the 78 cubic inches of air I had obtained to all the tests which could indicate its nature, and I found, much to my surprise:

(1) that it did not combine with water on shaking;

(2) that it did not precipitate lime water, but only caused in it an almost imperceptible turbidity;

(3) that it entered into no compounds with fixed or volatile alkalis;

(4) that it did not in the least diminish their causticity;

(5) that it could be used again for the calcination of metals; (6) in short, that it had none of the properties of fixed air: far from causing animals to perish like fixed air, it seemed on the contrary more suited to support their respiration; not only were candles and burning objects not extinguished, but the flame increased in a very remarkable manner: it gave much more light than in common air; charcoal burned with a flash almost like that of phosphorus, and all combustible bodies were consumed with astonishing speed. All these circumstances fully convinced me that this air, far from being fixed air, was in a more respirable and combustible, and therefore in a purer condition, than even the air in which we live.

This seems to prove that the principle which unites with metals when they are calcined and causes them to increase in weight is nothing else than the purest part of the air which surrounds us, which we breathe, and which during calcination passes from a condition of expansibility to that of solidity; if it is obtained in the form of fixed air from metallic reductions in which charcoal is employed, this is due to the combination of the charcoal with the pure part of the air, and it is very probable that all metallic calces would give, like that of mercury, only this eminently respirable air, if one could reduce them all without addition, as precipitated mercury is reduced....