Prof. J. Joly on the Apophorometer . 309 



may, in fact, easily be obtained from substances which 

 treated in the blowpipe would appear to afford none, as will 

 appear. The mode of procedure is as follows : — A circular 

 cover-glass — not too thin — grasped in a forceps, is held 

 horizontally above the platinum ribbon, as the temperature 

 is being raised. If the sublimate is one which oxidizes, we 

 obtain the oxidized sublimate alone ; or the unoxidized 

 sublimate bordered by the oxide, according as we hold the 

 glass further from or nearer to the ribbon. 



" The more volatile elements often afford as sublimates 

 both the element and an oxide of it. The elemental sub- 

 limate may often be obtained nearly pure by suitably 

 regulating the temperature. Thus, at low temperatures 

 arsenic sublimes as a rich grey-black sublimate, showing 

 the mirror when viewed through the glass. At a higher 

 temperature, especially if the glass is held at a distance of 

 three or four centimetres above the ribbon, the white 

 oxide — the trioxide — only is obtained. Sometimes both 

 element and oxide are together on the one glass, affording 

 an * eye,' the pupil of which is the element. This results 

 from the screening action of the outer parts of the ascending 

 column of vapour, the central parts being, in fact, sublimed 

 in the absence of oxygen, which is all absorbed in the outer 

 layers of the vapour. Magnesium, affords similar eyes sur- 

 rounded by the white oxide, or in many cases veiled over 

 by it, so that the dark metal is only seen through the glass. 

 The great avidity of this element for oxygen is shown in 

 this fact. Tin also affords ' eyes/ Thallium throws a rich 

 black velvety sublimate, fringed with deep ash-red (the 

 oxide ?). This is a very beautiful sublimate, but very 

 fleeting, the black soon fading into a pale greyish-brown 

 colour. If immediately enclosed from the air it retains its 

 original tints a longer time. Cadmium may also be sublimed 

 as the metal and its oxide. Indium affords a white sublimate, 

 dashed with pink and yellow. 



" While the metal is thus sometimes obtained with the 

 oxide it more generally affords the oxide only. This is the 

 case, so far as I have observed, with vanadium, lead, wolfram, 

 bismuth, tellurium, zinc, and antimony. But, again, some- 

 times the element appears to sublime without oxidizing. 

 Thus silver affords a grey-black veil of the metal, iridescent 

 where thinly deposited. Gold is also sublimed. Sulphur 

 is another case, the oxide being a gas at atmospheric 

 temperatures. Mercury gives a sublimate of a grey colour, 

 consisting of globules of the element. 



