534 Intellisence and Miscellaneous Articles. 



"to 



state and not melted by too strong a heat. It is not the lead alone, 

 but also the oxide of chrome, which absorbs oxygen. If oxide of 

 chrome alone be heated in oxygen gas, it is not converted into 

 chromic acid; but tliis takes place, as is well known, if an alkali be 

 present. I therefore consider that oxide of lead has the same effect 

 in this respect as an alkali. In order to obtain an intimate mix- 

 ture of oxide of chrome and oxide of lead, I endeavoured by means 

 of heat so to decompose the chromate of lead, that all the chromic 

 acid should be converted into oxide of chrome. The temperature 

 must be very high for this purpose, and it requires a long time be- 

 fore any considerable quantity of oxygen can be driven out of this 

 salt. 1"409 gi'amme was fused in a very thin platina crucible by 

 the strongest heat of a spirit-lamp before any appreciable loss took 

 place. 0"057 grm. were then given off equal to 4 per cent, which is 

 nearly j^j^jths of the whole quantity contained in it ; this would be 

 3"9 per cent. It is therefore very probable that at first the chro- 

 mate of lead is so decomposed that basic chromate of lead and 

 oxide of chrome are formed. 



2 (Cr O3 Pb O) = Cr O3 Pb. Oo + Cr O 1| -f- O l\. 



The compound obtained in this manner I considered very favour- 

 able for the conversion of chromic oxide into chromic acid. I heated 

 it, and passed a stream of oxygen through it. However, to my great 

 surprise, not the least alteration took place, and I found no increase 

 in weight. 



In the oxidation of the reduced salt, oxygen must have combined 

 with the oxide of chrome, as 6" 2 per cent, was in all absorbed, while 

 the whole of the oxygen of the oxide of lead in the salt amounts only 

 to 4' 89 per cent.; and it is not at all likely that even the whole of 

 this 4 "89 per cent, was absorbed by the reduced lead, as it was for 

 the most part fused into small globules, which must have very much 

 prevented the action of the oxygen upon it. 



I again fused 2'057 grammes of chromate of lead in an aether lamp 

 supplied with oxygen : after a long-continued heat it lost 0*091 

 grm. or 4*4 per cent. The reduction was in this case carried on 

 rather further than the conversion into basic chromate of lead and 

 oxide of chrome. When, however, oxygen gas was passed over 

 this compound very little of it was absorbed. 



I at last prepared an intimate mixture of oxide of chrome and 

 superoxide of lead ; this was heated to redness and oxygen gas 

 passed through it. This compound contained 0'445 g^m. oxide 

 of chrome. When the absorption had terminated, the increase of 

 weight was found to be 0*066 grms. The colour was changed from 

 green to brown. 0*455 grm. oxide of chrome contain 0*132 oxygen, 

 therefore just double the quantity it had taken up. Therefore one 

 atom of oxide of chrome upon heating with oxide of lead had com- 

 bined with 1^ atom of oxygen. 



This gives 2 Cr 3 O + 2 Pb O -|- 1^0, or, 

 Cr 03Pb, O, -l-CrOli. 

 It is therefore the same compound which is formed when chromate 

 of lead is fused by itself. 



It follows from the foregoing experiments : 



