In order to examine the relations which existed be tween the periods of evaporation and the production of electricity, M. Saussure made a great variety of expe riments. His apparatus consisted of a well-baked ves sel of clay, 4 inches in diameter, and 15 lines thick, which he insulated upon a clean and dry goblet of glass. Upon the vessel of clay he placed a crucible, or any other body powerfully heated, and by means of a wire he connected this crucible with the electrometer. Fifty four grains of distilled water were thrown upon the heated crucible, and by means of a time-piece and an electrometer he observed the period of evaporation, and the degree of electricity that was produced. The re sults which he obtained arc given in the following Ta bles.
The first column of all the tables contains the nmn ber of projections of water that were made. The second the number of minutes and seconds that had elapsed from the commencement of the experiment, or from the time of the first projection to that of the corresponding projection. The third column expresses in seconds the time which was necessary to reduce the 54 grains of distilled water to the state of vapour. The fourth ex presses in lines and tenths of a line, the distance of the balls of the electrometer. The fifth marks the character of the electricity which was produced ; and the sixth contains general remarks on the state of the crucibles, the vapours, and the noise which was made during eva poration. This noise undergoes great variations. It is almost nothing when the metal is very hot, and it in creases as the metal becomes colder, and dissipates more readily the projected fluid.
The following Table contains the results which were obtained, when the crucible was made of forged Iron, 2-1- inches in diameter, 22 lines high, 2+ lines thick, and weighing 25 ounces.
Saussure was greatly surprised at observing two such inflammable fluids as alcohol and ether following the same laws in their evaporation as water. The evapo ration was always greater at the time of the strongest heat, than when the heat was weakest. It then dimi nished to a certain point, and afterwards augmented till the heat was feeblest. In the ether too, the combustion had no sensible influence on the rapidity of the evapo ration.
Saussure now wished to observe the phenomena of evaporation in a crucible almost wholly shut. He there fore took a granade 31 inches in diameter, and brought to a white heat, and injected into it distilled water. A jet of brilliant flame was emitted from the mouth of the granade. A similar effect was produced at the follow ing projections, till the heated granade had the colour of a cherry ; but the brilliancy and heat of the flame diminished gradually with the heat. Saussure suppo ses that the flame arose from the inflammable air, produ ced by the decomposition of the water, or by that of the iron. Whenever there was any flame, there was no ap
pearance of electricity ; but as soon as the flame ceased, the electricity appeared. The electricity was always positive at the first experiment, but in the second it ap peared at first negative, and then nothing, when the small measure of water was projected into the granade ; but when half an ounce of water was thrown into it, the electricity was positive.
In order to explain the preceding experiments, 'AI. Saussnre supposes that the electricity is positive with those bodies that are capable of decomposing water, or of being themselves decomposed by their contact with the water, and that it is negative with those which are not decomposed or altered. This supposition was sug gested by the fact, that china and silver always produ ced negative electricity, while iron and copper gave po sitive electricity. If substances capable of being oxi dated, had constantly given a positive electricity, while those which do not oxidate had given a negative elec tricity, the preceding supposition would have acquired a great degree of probability ; but the phenomena have not always followed this law, a negative electricity being sometimes produced by the iron and the copper, and a positive electricity by the silver. Saussure re marks, that he was not much embarrassed by the first of these facts, for the iron and the copper are oxidated with great facility in a brisk fire, and become covered with a scaly crust, which, with the same degree of heat, is not susceptible of farther alteration. If this crust should therefore cover the bottom of the crucible, the drop of water will no longer be in contact with an oxi dable substance, and therefore no farther decomposi tion will take place, and consequently no farther gene ration of electricity. A part of the natural electricity, however, of the apparatus, will be absorbed by the va pours which are still formed, and therefore the appara tus will he electrified negatively. by any accident, some of the scales should be so far detached that the fluid will touch some parts of the metal, it may hap pen that the quantity of electricity thus generated com pensates exactly for that which the vapours absorb, and consequently the electricity will be nothing. If the scales are still more detached, the electricity will be su perabundant, and consequently positive. For the same reason a larger quantity of water gives constantly a po sitive electricity, when it is poured into an iron or cop per crucible, because it attacks the metal in a greater number of parts, and finds more easily the parts acces sible to its action. Hence, also, a strong positive elec tricity is produced when a mass of red hot iron is thrown into water, for the points of contact being more numerous, a more abundant decomposition takes place.