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POPULAR SCIENCE REVIEW. 
greenisli crystal plate of a superior make from Germany, clianged. Samples 
of glass unaltered by three months’ exposure nevertheless afterwards dis- 
coloured, and only one sample — an American sheet of ordinary blue glass — 
remained unaltered by twelve months’ exposure. In conclusion, Mr. Gaffield 
states that all this is due to carelessness on the part of glass-makers in their 
choice of materials not chemically pure. The sand, the carbonate or sul- 
phate of soda, and the lime, one or all, contain slight impurities of iron, the 
protoxide of which gives glass a green colour. To correct this, after the 
batch is partially melted, a little oxide of manganese, called glass-maker’s 
soap, is put into the crucible; some of the oxygen of the manganese flies off 
to the iron, and converts the protoxide into peroxide of iron. The peroxide 
gives a yellowish colour to the glass, and this, being complementary to the 
natural pink of the manganese, is neutralised, and the glass is thereby made 
of a light colour. When the sunlight acts upon glass thus made, the nice 
equilibrium between the oxygen of the iron and the manganese is disturbed, 
and sometimes the yellow, and sometimes the pink or purple colour is pro- 
duced.” 
Test for Methyl . — An eminent collodion manufacturer, writing to the 
Illustrated Photographer, sava verv rightly : Methyl has no business to be 
in collodion ; ” but adds, yet I do make methylated collodion for photo- 
graphers, because they will have a cheap article It is very easy to 
destroy the smell of methyl, so that the spirit cannot be detected by that 
sense ; but it is not so easy to make a wood spirit inert towards nitrate of 
silver.” The writer gives in conclusion the following test for methyl in 
ether, or alcohol supposed to be purely ethylic : Distil over into a test- 
tube a little of the suspected spirit, add a drop or two of solution of corrosive 
sublimate (very weak), then add excess of caustic potash. If the precipitated 
oxide is not redissolved, wood spirit is not present.” 
New Dry Process . — Mr. Carey Lea, in a recent number of the British 
Journal of Photography, gives the following new dry process : A plate is 
coated with collodio-bromide, and is thrown as soon as set into a bath of 
acetate of lead, acetic acid, and gallic acid. It is then simply dried without 
any other treatment, and so gives an excellent dry plate, very sensitive, and 
giving satisfactory negatives.” 
The Photographic Society. — The council of the London Photographic 
Society has published its annual report of assets and liabilities, without pre- 
viously submitting it to the members at the annual meeting. This is a 
somewhat unusual step. The balance sheet, too, is somewhat unusual, for 
it puts forward as satisfactory, statements proving that the society can only 
be regarded as solvent by those who accept a back stock of old and valueless 
journals, as worth 100/., and unpaid fees and subscriptions as worth 58/. 17s. 6d. 
Yet a member of the council, writing as editor of a weekly contemporary, 
says : We have no hesitation in asserting that the society is in a healthy 
and promising condition.” The members should take a more active interest 
in these matters than they appear to have done, for each is, we believe, 
individually legally responsible for the society’s debts. 
Photogra 2 :)hs of Eminent Men . — There are, doubtless, many of our readers 
who are desirous of obtaining the photographs of men distinguished for their 
devotion to science. This circumstance induces photographers to publish 
