2-28 On the Stonvs said to have 



solved oxide of mercury' to the metal not oxidated, which, 

 accovditiK to the above principles, must be abundantly taken 

 up. This effect continues till all the oxide of mercury in 

 the solution is brought to the utmost degree of oxidation. 



Sd> By this process, therefore, the whole of the dissolved 

 oxide of mercury i^ reduced to a uniform low degree of 

 oxidation, and the solution thereby rendered proper for pro- 

 ducing, from the beginning to the end of the precipitation, 

 black oxide of mercury. 



4th. The reason why the boiling solution is immediately 

 poured into a large quantity of water is, because on cooling 

 most salts crystallize from their solution, and are then dit- 

 ficult to be dissolved. But should the whole solution crys- 

 tallize during the process by too great evaporation of the 

 water, it would be necessary to add some nitrous acid, di- 

 luted with the necessary quantity of water, to dissolve the 

 whole by boiling, and then to proceed as before. 



The whole cannot be again dissolved by water, because 

 during crystallization a part of the nitrate of mercury is 

 decomposed, and the separated oxide of mercury is so much 

 oxidated ihat the remaining nitric acid is not iu a condi- 

 tion to bring it to a clear solution. 



5th. The pressing of the precipitate contributes in a con- 

 siderable degree to the speedier conclusion of the whole pro- 

 cess, because during the operation of drying a strong heat, 

 in consequence of the reasons before mentioned, cannot be 

 emplo\'cd. Whcii the moist as well as the dry black oxide 

 of mercury is exposed to a temperature which approaches 

 that of boiling water, its black colour is changed to gray, 

 and if the temperature be still further raised it becomes en- 

 tirely white; nay, by a still higher temperalure it soon as- 

 s<.mies an orange colour : which, however, is an evident sign 

 of increasing oxidation. 7"he before -jiiaitioned degree of 

 heat must, therefore, not be exceeded in the operation of 

 drying, and the precipitate must not even be washed with 

 hot water if it be required to obtain tliis preparation in the 

 proper state. 



XXXIX. On the Stones said to have fallni from the 

 Atmosphere. Bij J. Delalamje. 



X HF. Sitone> which fell near Laigle on tl^e CGth of April 

 lb03 have afforded considerable occupation to philosophers. 

 As a globe of lire which burst with a great noise had been 

 seen, it appears to me tliat this phtcuonieuja may be 



relerrr-d 



