126 M. Ulex on Slruvite. 



They cleave parallel to the plane of O. A peculiarity in 

 these crystals is, that they occur almost always in halves, and 

 appear to have rested or been formed on planes which would 

 have passed through the centre of the entire crystal. One of 

 these natural segments is shown in fig. 2. 



The crystals are transparent, and of a somewhat yellow 

 colour; most of them inclose organic matter, and are thereby 

 rendered more or less dark and opake. They are harder 

 than talc, but are scratched by gypsum. Their specific gra- 

 vity is 1*7. 



They are very sparingly soluble in water, and in conse- 

 quence tasteless. When heated in a tube they give out much 

 water and ammonia (the black crystals empyreumatic water 

 and ammonia) without flying into pieces. When heated to 

 redness, they exhibit the phenomenon of phosphorescence : 

 the passing of c into b, phosphoric acid. Heated before the 

 blowpipe they melt into a colourless glass, which on cooling 

 forms a white enamel. 



The constituent parts of the salt are phosphoric acid, mag- 

 nesia, ammonia and water. 



Dissolved in hydrochloric acid and precipitated by am- 

 monia, they yield a sandy powder, which under the micro- 

 scope exhibits the well-known form of the phosphate of am- 

 monia and magnesia. 



The salt loses by ignition 54"7 to 55'5 per cent, (the differ- 

 ence is caused by the small quantity of organic matter). The 

 ammonia was estimated by means of chloride of platinum; by 

 dissolving the salt in hydrochloric acid, 6*9 to 7'1 per cent, of 

 ammonia were found. The residue of 44'5 to 45'3 per cent, 

 should be the same combination of phosphoric acid with mag- 

 nesia as is contained in the phosphate of magnesia and am- 

 monia, because if the crystals are dissolved in hydrochloric 

 acid and precipitated by ammonia, the fluid which is filtered 

 from the precipitate gives no reaction either with sulphate of 

 magnesia or with phosphate of soda. It consists therefore of 



(NH 4 0) + 2MgO + P0 5 ) + 12HO. 



The crystals are the same salt which is found in many ani- 

 mal secretions, and in putrifying urine. 



The salt is not altered by the air. Mr. Graham has in- 

 formed us, that if the artificial salt is heated to 212° F. it 

 loses 10 at. of water and no ammonia. The natural crystals 

 can bear a temperature of 248° F., and they give out the same 

 quantity of water and no ammonia. The products of distilla- 

 tion were conducted into a solution of the nitrate of the pro- 

 toxide of mercury, which wa& not blackened. 



