218 ANNUAL OP SCIENTIFIC DISCOVERY. 



in a water-bath to dryness, being afterwards heated gently to drive 

 off any excess of acid. The residue was treated with strong sulphuric 

 acid, and allowed to stand several hours in order to convert the pyro- 

 phosphate of soda into the ordinary tribasic salt. It was then care- 

 fully diluted, neutralized by ammonia, and precipitated as ammonio 

 phosphate of magnesia ; the weight of the salt after ignition was .0701 

 grammes, equal to .045 of phosphoric acid. The consequent loss of 

 phosphoric acid in this experiment was 58.66 per cent. Another ex- 

 periment, in which the chlorine, instead of the phosphoric acid, was 

 determined, gives as the loss of acid 53.36 per cent. .2 grammes of 

 phosphate of magnesia and ammonia were next taken, dissolved in hy- 

 drochloric acid, diluted until about a gill of fluid was obtained, and the 

 whole was then evaporated as before. After precipitation and ignition, 

 the residue weighed .1315, corresponding to 41.69 per cent, of phos- 

 phoric acid. The percentage of phosphoric acid in the ammonio- 

 phosphate of magnesia, as determined by ignition, was 48.37 per cent. 

 Consequent loss of phosphoric acid, 6.67 per cent. Another experi- 

 ment, conducted in the same manner, with the exception that the pyro- 

 phosphate of magnesia was converted into the tribasic condition, by 

 fusion with carbonate of soda, gave 8.35 per cent, as the loss. The loss 

 of phosphoric acid, when the solution was acidified with sulphuric acid 

 instead of hydrochloric acid, was greater, probably owing to the higher 

 degree of heat required to volatize that acid. There was no percep- 

 tible difference between the action of hydrochloric and nitric acids. 

 Phosphate of soda was completely converted into the sulphate of the 

 same by three evaporations with sulphuric acid and water. Phosphates 

 of alumina, iron, lime, and magnesia, were not perfectly converted into 

 sulphates, even by a dozen successive evaporations. Phosphoric acid 

 does not seem to be more volatile in the vapor of alcohol than in that of 

 water. These experiments serve to show that the ordinary methods 

 of analysis are not applicable to the analysis of phosphates, which 

 must be dissolved in acid by the aid of heat. In the ordinary evapo- 

 rations to separate silica by rendering it insoluble, a very considerable 

 loss of this acid is occasioned. The estimated quantity of phosphoric 

 acid in ashes, c., must probably, in many cases, be much too low, 

 owing to this loss from volatilization ; and we may believe that, for 

 this reason, many analyses must be regarded as almost valueless, with 

 respect to the amount of phosphoric acid which they indicate. 



NEW ALLOTROPIC MODIFICATION OF PHOSPHORUS. 



SCHROTTER has demonstrated that the change of color produced in 

 phosphorus by the action of light is independent of the presence of 

 oxygen ; that it occurs even when the phosphorus is surrounded with 

 an atmosphere of pure dry hydrogen, carbonic acid, or nitrogen; and 

 that it is due simply to the passage of the element into an allotropic 

 state or form. Precisely the same change was produced by exposing 

 phosphorus for some time to a temperature of 226 C. ; the mass assumed 

 a fine red color, and became gradually less fluid, darker, and finally 

 perfectly opaque. The precise temperature at which the change takes 



