07i the Atomic Weight of Carbon. 217 



remains ; this is rubbed to powder, and digested in water 

 with twice its weight of neutral nitrate of lead for some hours; 

 the liquid is then poured off'. The oxide is by this means 

 converted into the basic nitrate (2 Pb O + N 5 ), which is 

 dissolved in boiling water, the solution filtered whilst boiling 

 hot, and then allowed to cool, when fine scaly crystals are 

 deposited. These were collected, washed, pressed into a 

 consistent mass, and dried. The mother liquor of these 

 crystals contains a still more basic salt, which precipitates 

 on mixing it with a solution of the neutral nitrate. The 

 liquid decanted at the commencement of the process, was 

 therefore treated in this manner in these experiments. The 

 last precipitate, which is pulverulent, was thrown upon a 

 filter, and allowed to drain, and, whilst yet moist, the inside 

 of a platinum crucible was coated with it to the extent of half 

 a line in thickness. This coating, when dry, adheres strongly 

 to the crucible. Since this basic salt does not fuse at the 

 temperature required completely to decompose it, there is 

 formed in this way a quantity of oxide of lead, which it is 

 true contains platinum when in contact with the vessel, but 

 the inner portions are quite free from that metal. In the 

 crucible thus lined, the basic salt is laid in single pieces, so 

 that after the calcination is completed, the oxide can be re- 

 moved without any admixture of that lining the vessel; for the 

 crucible containing the salt is, previous to the calcination, put 

 into a larger one, having a cover, and the whole is then placed 

 in charcoal, and heated to redness, at which temperature the 

 oxide does not fuse. It is very easily known when the salt is 

 entirely decomposed, for it is first converted into minium, 

 which appears almost black when red-hot; the smallest par- 

 ticle of it can therefore be plainly distinguished. After this 

 change is completed, the heat is continued for a full half- 

 hour, and then the crucible is removed. The oxide thus ob- 

 tained is of a beautiful lemon-yellow colour, and it does not 

 in the least adhere to the coating. It still possesses the glis- 

 tening appearance of the decomposed scaly crystals. It 

 dissolves in dilute acetic acid without changing the colour of 

 that liquid in the smallest degree, or leaving any residue, 

 which proves that it contains no minium. The solution, 

 moreover, is not rendered turbid by the addition of nitrate of 

 silver. 



" When this oxide was dissolved in nitric acid, precipitated 

 by sulphuric acid, the filtered acidulous liquid concentrated, 

 and the excess of sulphuric acid expelled, sulphate of lead 

 remained behind, from which water did not extract any traces 

 of a copper salt, and it was neither coloured nor rendered 



