1 3 1 feed, which is better; 6. Apiece or fome.pounded quick-lime, in a well-ftopped glafs, in order to make occafionally a folution of quick-lime ; 7. A phial with quickfilver; 8. A piece of infpilfated fuccus helioiropii, commonly called litmufs, or fome linen rags, tinged by being rubbed with the red part of long radiflies. The water employed in the various experiments muft be diftill.ed, and alfo quite pure; becaufe it would be importable to make any eftimate with certainty of the conftituent parts of the fubftances tinder examination, if a water Were tifed impreg nated with any other particles. The operator muft always be careful to avoid the fumes arifing from fubftances which afe brought into the fire; and therefore either have a chimney that draws well, or, when operating in-the open air, ftand in fuch a manner that the wind may carry off the noxious fumes. I fuppofe the pureft parts of the fubftances re quired to be examined will be employed, and care ufed to take fuch as are homogeneous, or nearly, as they will be beft fuited for the experiments, and to afcertain the quality of a fubftance under examination; I have often given more than one experiment on the fame fubftance: This was done, when I either thought the one character refulting from the one experiment not fufficient to afcertain the fubftance under examination, or when more fub ftances under the fame circumftances would have the fame phenomena.' It will therefore be right to take as many proofs as pofiible, before you clafs or range a fubftance under a cerrain genus. Some times, however, 1 have given feveral methods of allaying the fame fubftances; that, in default of one or other material ncccfiary for the experi- B 2 ment,