11 Prof. Hughes on the Physical 



Miscellaneous Notes. 



§ 183. The following notes of salts which have not yet been 

 fully examined may be useful. 



Cyanide of Potassium, as a cryogen, gives a temperature of 

 — 21°*1. The cryohydrate forms at — 33°, with a carbonic- 

 aeid and-ether cryogen. Compare § 170. 



Oxalate of Sodium forms a cryohydrate at — 1°*7 C. 

 Employed as cryogens, the following temperatures were 

 obtained from the corresponding salts : — 



o 

 Chloride of cadmium . . . — 8*3 C 



„ nickel .... —10*35 



Citrate of sodium .... — 11*3 

 Acetate of calcium . . . . — 11*8 

 Chloride of cobalt .... — 15'35 

 „ manganese . . . —28*0 



Those of these bodies which evolve heat on mixture with water 

 would, when cooled, depress the temperature more. Thus the 

 chloride of manganese scarcely showed signs of a cryohydrate 

 at -40° C. 



Formate of Sodium, as a cryogen, gives — 14 0, 3. A con- 

 centrated solution becomes semisolid at —14°, but does not 

 become opaque or completely solid in a salt-ice cryogen 

 (-22°). 



Tannic Acid, as a cryogen, gives — 1 0, 5. 



Sulphurous Acid gives a cryohydrate at — 1 0, 5. 



Boracic Acid, as a cryogen, gives — o, 8. The cryohydrate 

 forms at — 0°*7. 



Arsenious Acid.— The cryogen stands at — 0°'3 ; the cryo- 

 hydrate formed at — o, 5. Two samples of the melted and 

 liquid cryohydrate were sealed hermetically. After two or 

 three days it was found that a considerable quantity of a fine 

 white powder had exhibited itself, 



[To be continued.] 



V. On the Physical Action of the Microphone. 

 By Prof. Hughes.* 



IN the paper read on the 9th of May before the Eoyal 

 Society, I gave a general outline of the discoveries 1 had 

 made, the materials used, and the forms of microphone em- 

 ployed in demonstrating important points. I have made a 

 great number of microphones, each for some special purpose, 

 varying in form, mechanical arrangement, and materials. It 

 * Communicated by the Physical Society, having been read June 8, 1878. 



