144 PROFESSOR CALVERT OX THE 



ammoniacal quintibasic nitrate of lead, greenish-yellow 

 crystalline powders are produced, which are separated by 

 the mode above described, well washed in close vessels 

 with spirits of wine, and dried in vacvo. Although I 

 prepared these products for many months, and analyzed a 

 great number, still they vary so much in composition that 

 I am in doubt as to their true formulae. At all events, they 

 present this peculiarity, that even when they have been 

 boiled for weeks with renewed ammonia, well washed and 

 dried over sulphuric acid, they still gave off water, ammonia, 

 and nitric acid, the latter of which, most strange to men- 

 tion, I was unable entirely to remove. I am consequently 

 led to conclude, that the affinity of nitric acid for oxide of 

 lead is nearly equal to its affinity for ammonia. I have 

 little doubt as to the same fact existing with other com- 

 pounds of lead, as I obtained with the acetate and chloride 

 similar results as with the nitrate. I propose to name these 

 salts nitrated plumhates of oxide of ammonium, as they 

 differ entirely from the preceding not only in their greater 

 density, in their colour, in their slow solution in acetic, sul- 

 phuric, and nitric acids ; but also in giving off ammonia 

 and water when heated, and becoming of a light red. If 

 heated still higher, they decrepitate and give off nitric acid ; 

 left to cool, a beautiful crystalline yellow massicot remains. 



CONCLUSIONS. 



I. In this memoir are described four new isomeric prot- 

 oxides of lead, three of which are crystallized — one olive, 

 one red, one pink, and the fourth amorphous and of a 

 fine red. I believe I have demonstrated by this latter, that 

 the colour of red lead has been improperly attributed to a 

 small proportion of binoxide of lead which would exist 

 combined in red lead, and have clearly shown that the 

 colour of red lead is due to a molecular change which 

 massicot undergoes in the oven under the influence of heat. 



