150 Prize Essays proposed by the 



several chemists ? 2d, Of what orfranic substances do we already know, with 

 certainty, from authentic experiments, the proportion of their first principles. 

 3d, What advantage is this new method of analysing the above mentioned sub- 

 stances capable of imparting to the advancement of science ; or what may be 

 expected from it in future ? 



M. Thenard having found the means of combining water with large quan- 

 tities of oxygen, and the liquid which is obtained possessing very peculiar pro- 

 perties, which are si ill in a great measure inexplicable; there is desired a me- 

 moir, in which, after a reiterated and careful examination, the properties of 

 this liquid may be accurately described, and that an explanation, jjroved by 

 experiments, be given of them ; and in which it be also examined to what use- 

 ful purposes this fluid might probably be applied, whether in medicine or 

 otherwise. 



As several species of mollusca, especially those which are found in the sea, 

 are frequently employed among different nations ; and as, according to the ac- 

 counts that we find of them, wholesome, and even delicious, food is prepared 

 from them ; while of the mollusca which inhabit the sea near our coasts, there are 

 only used oysters, mussels and sea-slugs ; it is asked, What other mollusca, 

 which do not occur at a great distance from our coasts, may be reasonably es- 

 teemed as good for food ; and in what manner may it be tried whether they 

 might furnish as wholesome as agreeable a food ? 



A violent propulsion of the sap in poplars, combined with the expulsion of 

 a considerable quantity of air, having been observed by Coulomb, in April 

 1796, when he had perforated to the centre trunks of poplars, from four to 

 five decimetres thick, does not appear to have excited other philosophers to 

 repeat the experiment ; and as this phenomenon is, notwithstanding, very 

 worthy of being attentively examined, and as a careful investigation might 

 perhaps give rise to interesting discoveries, the society promises the gold me- 

 dal to him who shall take advantage of a favourable opportunity of repeating 

 this experiment in spring, on the trunks of various kinds of trees, and of 

 carefully observing all that may present itself in this phenomenon. 



There may be expected for an approved answer, besides the gold medal, 

 a gratuity proportionate to the interest of the results elicited by a careful 

 examination. 



Considering that the chemical experiments in Holland, especially tiiose of 

 P. Driessen, have shewn that the properties of atmospheric air near tlie sea, 

 are more or less modified or altered by the muriatic acid which it contains ; 

 and that, in particular, the solubility of lead in water is thereby augmented ; 

 that, however, these observations have not been confirmed in other places, 

 and that it is still required to be known if that acid exists quite free in the 

 air, or in chemical combination with other substances, the society desires — 

 That this subject be treated anew, and that it be tried by exact experiments 

 to demonstrate, if, in these countries, the atmospheric air contains muriatic 

 acid, what are the circumstances which augment its quantity, in what state 

 it occurs in it, and to what degree the quantities of the air may be altered 

 by it? 



As several substances, which were formerly known only in the state of gas, 

 may, through pressure and intense cold, be reduced to the solid or liquid form. 



