462 Intelligence and Miscellaneous Articles. 



used, the same facts would hold good ; or, if the anterior face 

 of the prism were covered by a screen, so as to expose a nar- 

 row fissure parallel to the axis of the instrument, would there 

 be found in the spectrum it gave every colour in every part, 

 as in Sir David Brewster's original experiment?" 



As my experiments were not made upon spectra formed 

 upon screens by prisms with large refracting surfaces, they 

 are not liable to this criticism, even if it were otherwise well- 

 founded. The spectra which I use are so pure, and free from 

 all commixture, that Fraunhofer's black lines are distinctly 

 visible; and the results are precisely the same when the re- 

 fracting face of the prism is reduced to the smallest possible 

 dimensions. 



My analysis of the spectrum by absorption, therefore, does 

 not indirectly controvert the principle, that " to a particular 

 colour there ever belongs a particular wave-length, and to a 

 particular wave-length there ever belongs a particular colour," 

 as Dr. Draper states, in theoretical language, the well-known 

 proposition of Sir Isaac Newton, but it directly controverts it, 

 and absolutely/ overturns it. 



St, Leonard's College, St, i\ndrews, 

 May 13, 184/. 



LXXI. Intelligence and Miscellaneous Articles. 



ON THE PREPARATION OF THE AMMONIACO-MAGNESIAN PHOS- 

 PHATE FROM URINE. BY M. BOUSSINGAULT. 



''r'HE author remarks that some time since Mr. Stenhouse proposed 

 -^ a process for i-endering the phosphoric acid and alkaline phos- 

 jihates contained in urine useful in agriculture. It is indeed suffi- 

 cient to add milk of Ume to it, to occasion a precipitate of phosphate 

 of lime. 



It occurred to M. Boussingault that it was possible, by means of 

 a magnesian salt, to collect both the phosphoric acid and a part of 

 the ammonia developed during the putrefaction of the urine ; and 

 the result was that of obtaining a manure which contains two sub- 

 stances useful to vegetation — phosi)horic acid and ammonia. 



In the month of June M. Boussingault mixed a solution of hydro- 

 chlorate of magnesia with about 123 pounds of urine, fresh collected 

 in the morning. At the end of five days the urine assumed a milky 

 appearance, and from this time the deposit of ammoniaco-magnesian 

 phosphate increased rapidly. A month afterwards the solution was 

 ])oured off, and the phosphate was collected on a cloth to wash it. 

 The salt was very white, and in small well-terminated crystals ; when 

 dried in the air, it weighed about one pound and nearly 100 grains 

 avoirdupois. The presence of the magnesian salt greatly diminished 

 the infectious odour emitted by the putrefying urine. It will be ob- 



