Intelligence and Miscellaneous Articles. 



397 



substances are elements, and some are chlorine, fluorine, and sulphur 

 compounds. I have found that not only all chlorides, but also bro- 

 mides, iodides, and fluorides of the simple substances, and also a 

 number of sulphides which could be obtained in a state suitable for 

 this investigation, have the property of transmitting a considerable 

 proportion of the heat from lampblack. These substances have also 

 something in common as regards their thermocrose. 



The numbers in the following Table give the transmitted heat in 

 percentages of the value of the deflections of the reflecting galvano- 

 meter produced by direct radiation. 



Transmitted heat. 



Thickness, 

 in miHims. 



Lampblack 

 at 100°. 



Gas-flame. 



Chloride of silver (AgCl) 



Bromide of silver (AgBr) 



Bromide of potassium (KBr) 



Iodide of potassium (KI) 



Cryolite (Al 2 Na 6 Fl 12 ) 



Zincblende (ZnS) 



Sulphide of arsenic with sulphur, As 2 S 



>> >> >> 

 Vitreous selenium 



3 

 3 

 3 

 3 

 10 

 5 



08 

 3 

 0-4 



per cent. 

 46 

 45 

 16 

 11 

 7 

 29 

 21 

 8 

 50 

 16 



per cent. 

 30 

 42 

 13 

 10 

 23 

 23 

 26 

 12 

 36 

 5 



Most of the substances were not quite homogeneous ; so that part 

 of the heat must also have been lost by diffusion and by reflection. 



Chloride of silver and bromide of silver are obtained, by fusion in 

 an atmosphere of chlorine or bromine respectively, as perfectly trans- 

 parent masses, which by being again fused between thin glass plates 

 acquire smooth surfaces. The salts adhere to the glass with extra- 

 ordinary tenacity ; heated concentrated nitric acid, which does not 

 perceptibly attack the salts, ascends by capillary attraction between 

 the glass and the silver-salt and separates them. Chloride of silver 

 appears perfectly colourless, bromide of silver of a clear amber colour. 



Chloride of potassium, bromide of potassium, and iodide of potas- 

 sium give, when fused, perfectly transparent masses, if the substances 

 are used in clear crystals as obtained by evaporating their solutions 

 at ordinary temperatures. A clear bright yellow plate of zincblende 

 was used which Professor Rose gave me for investigation ; the cryolite 

 plate used was turbid in consequence of numerous fine cracks and slits. 



Vitreous selenium is obtained in flat plates by fusing and pressing 

 it between glass plates. Plates of less than 1 millim. thickness 

 only transmit a narrow band in the extreme red of the solar spec- 

 trum ; plates of more than 2 millims. thickness are scarcely per- 

 ceptibly penetrated by intense sunlight. 



Plates of mixtures of arsenic sulphide with sulphur are also ob- 

 tained in the same manner. These mixtures, when they contain at 

 most three parts of sulphur to one of sulphide of arsenic, solidify to 

 amorphous softmasses, which only become hard and brittle after weeks. 



