594 REPORT — 1881, 



rature low ; this is the case, for instance, when 80 millia-rams of chloride of ammo- 

 nium are present in one litre, the column of the liquid four or five inches in depth, 

 and the temperature about 15° C. Under such circumstances only a trace of 

 nitrous acid is formed, and this changes into nitric acid before the conclusion of the 

 action. If the solutions employed are much more concentrated, or the temperature 

 is considerably raised, large quantities of nitrous acid are produced ; this formation 

 of nitrous acid may be avoided to a great extent by diminishing the depth of the 

 solution, l)ut at the temperature of 30° it is very difficult to avoid the foi'mation of 

 considerable quantities of nitrous acid, even with small depths of solution. In all 

 cases in whicli soil has been used as seed, the nitrous acid formed exists only 

 temporarily in the solution, the final product of the fermentation being always 

 nitric acid. 



Soil added to a solution of nitrite of potassium, supplied with nutritive ingre- 

 dients, readily converts the nitrite into nitrate. 



When solutions, whicli have been seeded with soil and undergone the nitric 

 fermentation, are themselves employed as seed for new solutions of ammonia, the 

 final result as before is nitric acid ; but this is apparently true only when the solu- 

 tion used as seed is not at most more than a few months old ; beyond this age the 

 result of the fermentation is apparently only nitrous acid, and this nitrous acid does 

 not further change into nitric, even in several years, unless a certain visible change 

 occurs in the solution to be presently mentioned. AVhen a solution which has 

 undergone this nitrous fermentation is used as seed, it again produces a purely 

 nitrous fermentation, the nitrous acid being constant as before. The iritrous ferment 

 just described is without effect on nitrite of potassium. 



The results just mentioned are perfectly in accordance with the facts recently 

 published by Pasteur, who finds that by allowing the cultivation of an organism 

 (as that producing chicken cholera) to become old, an organism is obtained of 

 diminished energ;y, which when cultivated continues to produce organisms of the 

 same diminished energy. 



If solutions which have nitrified are kept for a considerable time, a white 

 organism not unfrequently appears in spots on the surface of the liquid, and under 

 favourable conditions spreads over the whole surface. Viewed by a lens it appears 

 as a mass of interlaced fibres. This organism has been examined microscopically 

 by Dr. M. Masters, F.R.S., and more fully by Professor E. Ray Lankester ; both 

 pronounce it to be a bacterium. Wherever this surface organism appears, any 

 nitrites that may be present are speedily converted into nitrates; a solution of 

 nitrite of potassium is also speedily converted into nitrate. The experiments as yet 

 made with this organism leave it doubtful whether it has any power of oxidising 

 ammonia ; this part of the subject requires, however, further investigation. There 

 can be little doubt that this surface organism is a stage in the development of the 

 nitrifyiiig ferment. 



The nitrifying ferment appears capable of existing in two, or perhaps three, con- 

 ditions, producing definite chemical eflects : — 



1. Tlie nitric ferment of soil, which converts both ammonium salts and nitrites 

 into nitrates. 



!^. The altered ferment, which converts ammonium salts into nitrites, but fails 

 to change nitrites into nitrates. 



3. The surface organism, which changes nitrites into nitrates. 



3. On the Effect of the Specfmim of Silver GhloHde. 

 By Captain Abnet, E.E., F.R.8. 



In all works with which the author is acquainted, the maximum intensity of the 

 spectrum impressed on silver chloride is shown as situated in the indigo portion of 

 the spectrum. Owing to a recent investigation by Dr. Eder, of Vienna, the possi- 

 bility of developing an image on silver chloride by the alkaline developer, and by a 

 ferrous citrate developer, has become practicable. The old method of developing 

 by means of acid solutions was misatisfactory and tended to give false impressions. 

 The author experimented with chloride of silver prepared as an emulsion in gelatine.. 



