59 



vessel of lead or platinum, in Avliich finely powdered fluor spar 

 and sulphuinc acid have been mixed together into a paste. A 

 gentle heat being apphed, fmnes of hydrofluoric acid are given 

 off, which, coming in contact with the glass, produce the desired 

 effect in a few minutes. The wax or etching ground is then 

 washed off with oil of vitriol. 



Again, if equal parts of finely powdered fluor spar and glass, 

 or fine white sand, are mixed together, and water and sulphuric 

 acid added, hydrofluoric acid will be given off as before, but 

 coming in contact ^nth the silica of the powdered glass or sand 

 the acid will be decomposed, the result being water and a gaseous 

 fluoride of silicium, known by the presence of white fumes ; the 

 whiteness being caused by the presence of minute particles of 

 silex, arising from the decomposition of the fluoride on comino- in 

 contact with the aqueous vapour of the atmosphere, for it is an 

 accepted fact that, if the gaseous fluoride of silicium come in contact 

 with water, it is itself decomposed, and gives rise to silica and a 

 double fluoride of silicium and hydrogen called hydrofluor-silicic 

 acid. 



IntXiQ Quarter! ji Jourmd of Microscopical Sckiice for April, 1863, 

 there is an abstract of a paper by Max Schultze on " The stracture 

 I of the valves of diatoms, as compared with sihceous pelUcles 

 [produced by the decomposition of fluor silicic acid in moist air." 

 tThese pellicles, to which we propose drawing the attention of the 

 PSociety, are produced by a modification of the process last described, 

 rand certainly bear in their markings such a resemblance to the 

 f markings on the ^•al^■es of many diatoms as to warrant their being 

 [called " Artificial Diatoms." 



To make tlie Artificial Diatoms, described by Schultze, a 

 j modification of the last-named process is necessary. Take a well- 

 Icleaned Florence oil flask ; into tliis put about a teaspoonful of 

 powdered fluor 3par, and the same quantity of powdered glass. On 

 ttliis mixture poirsuSicient sulphuric acid to form athickish paste. 

 lln the Florence iask insert a loose plug of moistened cotton wooL 



