Analysis No. 2. Another portion of crystallized acid, prepared 

 and purified as above, was analysed with barium; 1-2345 grm. of 

 acid yielded, according to the second method already described, 

 1'2155 grm. of sulphate of barium, corresponding to 1-2363 grm. 

 of the monohydrate, or to 84'89 per cent, of ClG 4 H + H a O. 



The following gives the results of the analyses : 



(a) Composition of Crystallised or Monohydrated Perchloric Acid. 



Found. 



Calculated. I. II. 



C1OJI 100-5 84-80 84-55 84'89 



H 2 O 18-0 15-20 



118-5 100-00 



) Composition of the Potassium-Salt obtained from the crystal- 

 Used acid 



Cl 

 4 

 K 



The monohydrate of perchloric acid solidifies at the ordinary tern- 

 perature to long silky needle-shaped crystals, which fume strongly in 

 the air, most rapidly absorbing moisture, and immediately deli- 

 quescing on exposure. Placed in a thin bulb in a water-bath, the 

 liquefied acid was found to freeze between 49*5 and 50'0 C., whilst 

 the crystals melted between 50-0 and 51'0 C. ; hence the melting- 

 and freezing-points of this substance lie within a few tenths of 50 C. 

 The specific gravity of the liquid monohydrate at 50 C. is 1*811 ; 

 but the solid acid is considerably heavier, owing to the large con- 

 traction which the liquid undergoes on freezing. As has been 

 described, the monohydrate splits up on heating into real perchloric 

 acid and a less volatile aqueous acid ; it therefore possesses no 

 definite boiling-point. Heated to 110 C., the melted crystals 

 enter into rapid decomposition, which, when once commenced, con- 

 tinues for some time, even when the thermometer sinks to 95 ; on 

 further application of heat, the liquid becomes of a dark yellowish- 

 brown colour, ebullition continues, and the temperature gradually 



