304 Mr. Budamsona Scarlet Siib-chromute of Lead. [April, 



very diluted acetic acid. The red colour gradually but totally 

 disappeared, and was succeeded by a pure yellow. This yellow 

 powder, carefully washed and dried at 300", weighed 60 grains, 

 and proved on examination to be ooninion clironiate of lead. 



Here then we have red chromate of lead (said by Grouvelle to 

 contain exactly the same proportions ol" oxide and acid as the 

 yellow chromate) resolved into GO grains of yellow chromate and 

 40 grains of some other substance, which we shall see, by the 

 next experiment, to be oxide of lead. 



(B.) The acetic acid holding in solution 40 grains of the 

 original weight of the red chromate employed, was perfectly 

 colourless and transparent ; and, on being iiently evaporated in 

 a water bath, shot entirely into crystals, bearing the well-known 

 character of acetate of lead. On redissolving these crystals in 

 water, and boiling them with an excess of carbonate of ammonia, 

 a dense white precipitate fell, weighing, when dried, 4(i grains 

 = 38-45 nearly of oxide of lead.* 



(C) To ascertain whether any sensible jjortion of pDtash 

 originally entered into the composition of this red chromate, 

 the ammoniacal solution was evaporated gently in a large platina 

 crucible, and gradually exposed to a red heat : the whole resi- 

 due sublimed, leaving only a scarcely perceptible stain of lead 

 upon the surface of the crucible. A little vvater now boiled in 

 the same crucible did not affect the colour of turmeric paper in 

 the slightest degree ; hence no potash whatever can be sus- 

 pected. 



On repeating these experiments, I feel satisfied that the 

 40 grains of loss sustained by the red chromate in Experiment 

 (A), were entirely due to oxide of lead ; and that 100 grains of 

 red chromate were resolved into 60 grains of yellow chromate 

 and 40 oxide of lead. But 60 grains of vellow chromate are 

 composed of 40'98 oxide of lead, and 19*02 chromic acid ; hence 

 it cannot be doubted that yellow chromate contains just half the 

 proportion of oxide in the red chromate, in which case the 

 atomic constitution of the two chromates of lead will be 

 as follows : 



Yellow chromate. Red chromate. 



Chromic acid . . 19"0'2 1 atom Chromic acid 19-02 1 atom 

 Oxide of lead. . 40-98 1 atom Oxide of lead 81-96 2 atoms 



Or 100 parts consist of 



Chromic acid 3 Iv Chromic acid 18*84 



Oxide of lead 68-3 Oxide of lead 81-16 



100-00 100-00 



In order further to show the true composition of red sub- 



* The difference between 3S'45 and 40 is owing to the imperfect precipitation of 

 t)Xide of lead bv carboijate of ammonia. 



