Bauhaus-Universität Weimar

Optical Projection: A Treatise of the Use of the Lantern in Exhibition and Scientific Demonstration
Wright, Lewis
difficulty; as with these proportions, if the gas is ‘rushing,’ 
and the flame be lowered, the flow does not diminish for a 
minute or two. Hence the probable behaviour must be anti¬ 
cipated^ as it were. This needs experience, and the beginner 
should make his gas cautiously till he has gained it, which 
will only take him rather more time to fill his bag. Steadi¬ 
ness of action can, however, be attained by further adding to 
the mixture common salt, for which hint I am indebted to 
Mr. E. Holland. Take, say, 
Chlorate of potash ... 2 lbs. 
Manganese oxide .... £ lb. 
Salt ...... 6 ounces. 
In this mixture the chlorate is to be powdered as well as 
the other ingredients, and the evolution of gas will answer 
almost instantly to the lowering of the flame, and thus be 
under perfect control. This is therefore the mixture I recom¬ 
mend : chlorate, 8 parts by weight ; manganese, 2 parts ; salt 
1^ parts. 
When chlorate is used with manganese alone, it must 
not be powdered, but used in the rough crystals ; and 1 lb. of 
the chlorate—the only active ingredient—must be allowed 
for 4 to 4J cubic feet of oxygen. Powdered chlorate, without 
salt, is liable to cause violent rushes. It may also be noted 
that finely granulated manganese is better than powdered, as 
not choking the delivery-tube at all ; but it is seldom easy to 
procure, and the powder need cause no inconvenience. 
Using the necessary caution, it often happens that when 
the charge is about half exhausted the evolution of gas stops 
for a while, and even the full flame fails to start it again for 
some minutes. It will resume, however, and during this 
second stage there is little need of caution for fear of a rush ; 
the full heat is generally needed to the end. For its thorough 
manageability, however, I strongly recommend the salt mix¬ 


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