AND MECHANICAL CONDITION ON EADIANT HEAT. 87 



The effect of atomic complexity upon the radiation is well illustrated by the deport- 

 ment of these two substances. It is further illustrated by the deportment of two 



different iodides of mercury : — 



Badiation. 



Biniodide of Mercury (Hg Ig) . . . 39-7 

 Iodide of Mercury (Hg2 12) • • • 46-6 



Here the addition of a second atom of mercury to the molecule of the biniodide 

 raises the radiation seven per cent. The experiment furnishes a kind of physical justi- 

 fication of the practice of chemists in regarding the molecule of yellow iodide of mer- 

 cury to be Hg2 12, and not Hg I. 



The peroxide and protoxide of iron gave the follovmig results : — 



Badiation. 



Peroxide of Iron 78*4 



Protoxide of Iron . ...... 81*3 



I did not expect this, the protoxide being a less complex molecule than the peroxide. 

 On examination, however, the protoxide was found to be in part the magnetic oxide. 

 The formulae of the two substances are Fe^ O3 and Fe O, Fe2 O3, and the anomaly there- 

 fore disappears. 



Amorphous phosphorus and sulphide of iron gave the following results : — 



Radiation. 



Amorphous Phosphorus 63-6 



Sulphide of Iron '. . 81-7 



Sugar and salt were reduced in a mortar to the state of exceedingly fine powders. In 



point of cohesion and physical aspect these substances closely resemble each other ; their 



radiative powers, however, are as follows : — 



Radiation. 



Salt 35-3 



Sugar 70-0* 



In his last interesting paper on emission at a red heatf , M. Desains mentions oxide 

 of zinc as a body which at 100° C. has the same emissive power as lampblack. This is 

 nearly true for the hydrated oxide ; with the calcined oxide the following is the relation : — 



Radiation. 

 Lampblack ......... 84-0 



Hydrated oxide of Zinc 80-4 



Calcined 53-2 



* I have of course no intention of adducing experiments on sugar and salt, or on powdered rock-salt and alum, 

 as opposed to the results of Masson and CouErfEPiiE. They would regard their results as unaffected by such 

 experiments. It is the deportment of the chemical precipitates employed, and not that of bodies reduced to 

 powder by mechanical means, that invalidate their conclusions. 



t Ck)mpte8 Rendus, July 3rd, 1859; Phil. Mag. Aug. 1865. 



