582 



REPOET — 1886. 



are largely used, as, for instance. Turner's sun-light pictures, they should be kept in 

 a very subdued light, preferably of a yellow tint, such as is obtained by blinds of un- 

 bleached linen. For artificial illumination the arc-light is unsuitable, but incan- 

 descence lamps are preferable to gas, as yielding no products of combustion, which 

 in the case of gas are capable of causing injury. The action of the violet rays is 

 two to three times as powerful as the red or yellow ; and there is a great difference 

 between the action of diffused daylight sufficientlj' strong to view pictui-es, and direct 

 sunlight. Without exact measurements it is difficult to appreciate its magnitude, 

 but the latter may be safely set down as on an average forty times, and in summer 

 even probably four hundred times as great as the former ; hence a picture which 

 would fade in ten years in sun-light might be preserved for several hundred years 

 in a subdued yellow light. The author has not observed any destructive action of 

 light on grey tints made from mixtures of indigo and light red, even in sketches 

 painted as long as sixty years ago, by his fiither, and since exposed to subdued 

 daylight. The acidity in drawing paper should be corrected by a wash of a dilute 

 solution of borax, and in no case ought any paste or glue to be placed at the 

 back of a drawing for the purpose of mounting it. 



2. On the Distribution of the Nitrifying Organism in the Soil. 

 By R. Waeington, F.B.S. 



Previous experiments, conducted at Rothamsted on this subject (' Trans. Chem. 

 Soc. ' 1884, p. 645) had led to the conclusion that the nitrifying organism is 

 always to be met with down to 9 inches from the surface, and that at 18 inches 

 it is sometimes present ; but experiments with soil 2 to 8 feet from the siu-face failed 

 to yield evidence of the presence of the organism. 



Further experiments have been made in 1885, and during the present j'ear, both 

 in the field with the stiflT clay subsoil previously worked on, and in another field having 

 a loamy subsoil ; in all sixty-nine new experiments have been made. The soil in 

 the previous experiments was removed, with suitable precautions, from a freshly 

 cut surface, and placed in sterilised solutions consisting of diluted urine (0-4 per 

 cent.) It having since been found that the facility with which urine nitrifies is 

 greatly increased by the presence of gypsum ('Trans. Chem. Soc' 1885, p. 758), 

 an addition of a small quantity of gypsum was made to the solutions employed in 

 all the recent experiments ; rather larger quantities of soil were also employed. 

 The results may be summarised as follows: — 



Six of the above experiments were made with clialk, which underlies the 

 Rothamsted subsoil ; the chalk was from depths of 5, G, 7, and 8 feet. None of 

 the samples of chalk produced nitrification. 



The new results show a far deeper distribution of the nitrifying organism than 

 was concluded from the earlier experiments. The power of producing nitrification 

 is now found to exist generally down to 3 feet from the surface. Below this 

 point the occurrence of the organism becomes less frequent, though at 5 and 6 

 feet about half the trials resulted in nitrification. ' With soil from 7 and 8 feet 



