Prof. Magnus on the Propagation of Heat in Gases. 85 



small crystal of nitrate of silver, a yellow precipitate of phosphate 

 is at once obtained. In employing this test for phosphates, the 

 beginner should be cautioned, however, that silicates (if decom- 

 posable by carbonate of soda) will produce the same reaction, but 

 the silica may be eliminated by adding several drops of acid and 

 evaporating to dryness. By treatment with salt of phosphorus, 

 moreover, silicates are at once recognized. If the solution of our 

 mineral, as obtained above, be treated with acetate of lead, the 

 precipitate presents the well-known blowpipe reaction of phos- 

 phate of lead, *. e. the formation of a faceted globule without 

 reduction. 



Two analyses of the North Carolina lazulite are given by Pro- 

 fessors Smith and Brush in the ' American Journal of Science 

 and Arts' for September 1853. These exhibit the following 

 results : — 



I. II. 



Phosphoric acid .... 43-38 44-15 



Alumina 31-22 32-17 



Protoxide of iron .... 8-29 8-05 



Magnesia 10-06 10-02 



Water 5-68 5-50 



Silica (an impurity) . . . 1'07 1-07 



9970 100-96 



From the above values, Messrs. Smith and Brush have deduced 

 the annexed formula : — 



2[3(MgO ; FeO), PO 5 ] +5A1 2 3 , 3P0 5 + 5HO. 

 The true position of lazulite, in a natural classification, appears 

 to be amongst a group of phosphates containing both anhydrous 

 and hydrous species (the distinction between these being entirely 

 artificial), and in some of which fluorine is also present. In this 

 group I would place the following minerals : — Childrenite, Wa- 

 vellite, Fischerite, turquoise, lazulite, Wagnerite, Herderite, am- 

 blygonite, monazite, xenoiime, and cryptolite. 



Toronto, Canada, 

 June 20, 1861. 



XIV. On the Propagation of Heat in Gases. By G. Magnus. 



[Concluded from p. 12.] 



Passage of the Paijs of Heat through Gases*. 



AN objection might still be raised against any conductibility in 

 gases. It might be maintained that the stronger heating of 

 the thermometer in hydrogen depended on the fact that it per- 

 mits the passage of heat-rays more easily than all other gases. 

 * Read before the Academy of Berlin, February 7, 1861. 



