148 CHANGES PRODUCED BY THE SOLAR RAYS. 
The decomposition of the hydrocyanic acid under the in- 
fluence of the solar radiation is also due to the chemically 
active rays, and I have found that the change has been 
effected more speedily in the blue and indigo rays than in 
any others. We have in this case the formation of ammo- 
nia, and the precipitation of a brown powder which appears 
to be a compound of nitrogen and carbon. 
Such is a general outline of the results to which my re- 
searches have at present led me. It is a very common 
practice for Druggists and manufacturers to put those phar- 
maceutical preparations which are liable to change by light 
into dark purple coloured bottles, or to cover white glass 
bottles with blue paper, with the idea that the quan- 
tity of light admitted is then so small that no change 
can take place. We learn from these investigations, and 
the knowledge is of great practical importance, that no 
plan more efficient for producing rapid decomposition could 
be adopted than the use of blue glass bottles. Light posi- 
tively acts as an interfering agent — this light is obstructed 
by the dark blue glass, and the pure or nearly pure chemi- 
cal rays are permitted to act on the preparations with all their 
energy. If instead of using those kinds of bottles, others 
prepared of a neat form from the ordinary dark green bot- 
tle glass were adopted, there would be but little fear of any 
decomposition from the solar radiations. Not only does 
this kind of green glass obstruct the rays of light to a great 
extent, but nearly all the calorific rays are shut off, and the 
actinic or chemical rays are reduced in quantity and force 
in a very remarkable manner. 
For bleaching oils there can be no question but purple 
bottles would be by far preferable to any other colour for 
the reasons above explained. — Pharm. Journ. 
