Mixter — [Instable Chromium Sesquioxide. 297 



which added to the heat of the fusions. The effect of com- 

 bined water, for example, is that of free water less the heat of 

 combination of water with chromium sesquioxide. In fusions 

 with sodium peroxide water combines with the sodium oxide 

 formed. For 18 grams of free water the effect is 36,000 cal. 

 or 2,000 cal. per gram. Likewise for one gram of carbon 

 dioxide it is 1700 cal. The effect of the two in combination 

 with chromium sesquioxide is unknown but less. It is assumed 

 to be 1500 cal. Since the chromium sesquioxide contained 



Table I. 



12 3 4 5 



)\\0 % ignited 7*258 



" holding 5-9^ H 2 0-fC0 2 ___ 7-784 



" " 3-4$ " " ... 7-300 1-119 7-009 



" uncombined in fusion 0-066 0*0 0-030 0-044 0-043 



" combined in fusion (a) 7*192 7*784 7*270 7*135 6*966 



.ampblack 0*778 0*504 0-507 0*480 0*471 



ra 2 2 27* 23* 24* 25* 21* 



V r ater equivalent of system 4128 4198 4138 4132 4132 



'emperature interval 3*276 2*996 2*816 2*733 2*694 



[eat effect observed 13523 12577 11652 11292 11132 



" " of lampblack . _ —8273 —5360 —5392 —5100 —5010 



u u " iron wire —30 —40 —30 —40 —20 



" "Cr 2 3 (6)_ 5220 7177 6230 6152 6102 



" " 1 gram of CrO— 726 922 857 862 876 



2 3 a 



only small quantities of water and carbon dioxide, the error in 

 the assumed heat effect of these will make but little difference 

 in the value found for chromium sesquioxide. One gram of 

 substance used in Exp. 2 contained 0-059 gram of water and car- 

 bon dioxide, and 1500 c X 0*059 = 88. The observed heat 

 effect of the substance is 922 c , and 922 - 88 -*- 0*941 = 886. 

 From 865 cal., the mean of experiments 3, 4 and 5, 843 cal., is 

 derived. The average of 886 and 843 is 865 cal. for the heat 

 of the reaction of one gram of unstable chromium sesquioxide 

 with sodium peroxide. This is an approximate value, very 

 likely low since the oxide used may have contained some of 

 the stable oxide. In the former paper 52*1 was taken for the 



i. 



a 



