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POPULAK SCIENCE REVIEW. 
torial base may be recognised. The pure dye is easily separated from crude 
safranine. It is only necessary to exhaust the commercial product with 
boiling water ; on cooling, the filtrate deposits a slightly crystalline substance 
which, after several recrystallisations from boiling water, leaves no residue 
on ignition. During these operations, however, the salt undergoes perceptible 
alteration ; with every recrystallisation it becomes more soluble and less 
crystalline. These alterations depend upon the separation of chlorhydric 
acid from the salt. In fact the percentage of chlorine, is found to diminish 
in the product of successive crystallisatious ; thus the product of the third 
contained 8-48 per cent., that of the fourth crystallisation only 7-46 per cent. 
Addition of chlorhj^dric acid to the mother liquors at once reproduces a 
crystalline precipitate. This instability of the chlorhydrate, and in fact, as 
may even now be stated, of the salts of safranine in general, has very con- 
siderably impeded the study of this body, and often materially afiected the 
accuracy of the analytical results. In order to obtain the normal salt, the 
boiling liquid during the last crystallisation had always to be acidified with 
chlorhydric acid. The authors also describe rather fully the chlorhydrate, 
nitrate, sulphate, oxalate, and picrate of the base, but we have not space for 
a further abstract. 
The Sensitiveness of Collodion Films. — Dr. J. W. Draper has an interesting 
note on this subject in “Silliman’s American Journal” for January. He says 
that the silver compounds of collodion absorb the radiations falling on them, 
which are capable of producing a photographic effect. Yet sensitive as it is, 
collodion is very far from having its maximum sensitiveness, as is shown by 
the following experiment, which is of no small interest to photographers. 
I took five dry collodion plates, prepared by what is known as the tannin 
process, and having made a pile of them, caused the rays of a gas flame to 
pass through them all at the same time. On developing it was found that 
the first plate was strongly impressed, and the second, which had been behind 
it, apparently quite as much. Even the fifth was considerably stained. 
From this it follows that the collodion film, as ordinarily used, absorbs only 
a fractional part of the rays that can affect it. Could it be made to absorb 
the whole, its sensitiveness would be correspondingly increased. 
Pyrology, or Fire Analysis. — This is the subject of a series of interesting 
papers by Captain W. Koss, R.A., in the “Chemical News” [Feb. 1873]. 
They are too long for abstract, so we must refer our readers to the original. 
How to ascertain change of colour of Litmus in Alkalunetrical Assays . — 
A paper contributed to the “ Comptes Dendus ” of the French Academy 
[Jan. 27] by M. L. D’Henry gives a description of a Bunsen gas-burner so 
arranged that the flame is kept constantly saturated with sodium, so 
that while the blue colour of litmus appears deep black, the red colour 
produced by the addition of an acid appears as colourless as water; 
thus affording a better means of ascertaining the precise moment when 
the alkali is saturated. 
Hoiu the London Vestries look after Adulteration. — The scandalous system 
adopted by these bodies has been exposed in an able fashion in the “ Chemi- 
cal News,” Feb. 7. The writer of the article says that the vestries, for 
the sake of economy, offer a paltry lOOZ. or 150A a year to the salary of their 
medical officers to undertake the analyses. Now what is, generally speaking, 
