1892-93.] 
Mr Aitken on Breath Figures. 
97 
show some degree of whiteness when breathed on ; and it has been 
found that breath figures can be produced rather better on a surface 
of this kind than on clean glass. If the glass, after being cleaned, 
be subjected to the action of the blow-pipe flame, the jet being 
made to travel quickly over it to prevent breaking, and then cooled, 
the coin placed on it, and then heated, breath figures will be pro- 
duced, sometimes having great distinctness. The black parts being 
much blacker than when clean glass is used, sometimes these images 
on flame-treated surfaces do not require to be breathed on to be 
visible. The hot coin seems in some way to alter the dusty im- 
purities on the surface of the glass, and causes them at certain parts 
to reflect more light than at others, so that the image is visible 
without being breathed on, but it is further developed when breathed 
on. These experiments show that dust does play a part in some 
kinds of breath figures. 
Sometimes the impressions adhere very firmly to the glass, and 
are difficult to remove ; but generally their removal may be efiected 
by breathing on the plate, and by hard and frequent rubbing whilst 
it is wet. Water or alcohol may also be used with good results, 
but perhaps the most effectual means of destroying them is to pass 
over the surface of the glass either a blow-pipe or a Bunsen flame. 
VOL. XX. 
26/7/93 
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