446 Prof. E. Wartmann's Seventh Memoir on Induction. 



decomposition commences, the liquid touches the metal and 

 covers it, at the end of the operation, with a slightly adherent 

 coating, which is of a beautiful glossy black. This crust of 

 carbon, heated even until the naked parts of the capsule are 

 red, absolutely prevents the production of the spheroidal state; 

 but pure or sugared water which is let fall on theplatina, and 

 is coloured of a deep black colour by some particles of the 

 deposited carbon, behaves as if it had remained transparent 

 and colourless. 



207. M. Fechner states* that water no longer becomes 

 spheroidal when it has been tinged with ink, or rendered 

 opake by charcoal suspended in it. I repeated these experi- 

 ments with care, and have found them inaccurate. In the 

 two cases the blackened liquid readily assumed the spheroidal 

 state on a plate of platina, and remained so for several minutes, 

 until the solid particles from which it separates on evaporating 

 unite into a small spongy ballf. 



208. Moist crystallized sugar spheroidalizes whilst dissol- 

 ving in its water of crystallization. It presents the same phases 

 as the syrup from the moment of the caramelization. 



209. Butter and suet pass into the spheroidal state in melt- 

 ing : they soon take fire and give off a light soot which dis- 

 appears, being converted into carbonaceous gases. 



210. It is very generally thought at the present day that 

 one of the principal causes of explosion of boilers is owing to 

 the sudden conversion into gas, at a very high temperature, 

 of water first spheroidalized by contact with over-heated sur- 

 faces. If this opinion is proved, this terrible danger will cer- 

 tainly be remedied by clothing with an appropriate coating the 

 internal surface of the generators, or by giving it a rough 

 surface, which is unfavourable to the production of the sphe- 

 roidal state. This would be less costly, and would present much 

 less danger than the set of points proposed by M. Boutigny. 

 I have not had the means of making experiments on this sub- 

 ject, which I must postpone till a more propitious moment. 



* Repertorium der Physik, vol. ii. p. 401. German translation of the 

 Treatise of Experimental and Mathematical Physics of M. Biot, vol. v. 

 p. 367. 



f M. Boutigny has made an analogous observation on water containing 

 soot (work cited, p. 25). 



