454 MATHEMATICS AND NATURAL PHILOSOPHY. 



collodion film may be obviated. Many modifications of Shadbolt's original honey- 

 process have been proposed, and the use of various substances, such as glycerine 

 metagelatine, golden-syrup, oxymel, has been recommended, all adopting for their 

 basis the principle of washing off the free nitrate of silver after the plate has been 

 excited, and then covering it with the preservative syrup which keeps it moist 

 and prevents the small excess of free nitrate left on the collodio-iodide from dry- 

 ing and crystallising. Another plan, claimed by several originators, is remarkable, 

 consisting in leaving the excited plates in distilled water, when, if protected from 

 the light, they will retain their sensitiveness for weeks unimpaired. The most 

 promising however seems to be Taupenof s Albumen process (described in Can. 

 Journ., Vol. I., N.S., pp. 195) of which the following is the latest simplification, 

 as practised by Mr. H. P. Robinson. The Nitrate-Bath consists of: Mtrate of 

 Silver, 35 grs., Glacial Acetic Acid, 1 min., Distilled Water, 1 oz. Having coated 

 the plate with collodion, and excited as usual, let it be immersed for about one 

 minute in distilled water, then washed for two or three minutes under a tap, 

 allowed to drip for a minute, and then have poured over it some iodised albumen 

 which need only remain for a few seconds on it. This iodised albumen is made as 

 follows : Albumen, 1 oz. ; Distilled Water, 2 drachms ; Ammonia, 8 minims > 

 Iodide of Ammonia, 5 grs. ; Bromide of Ammonia, 1 gr. ; dissolve the iodide and 

 bromide in the water, and then add the ammonia to the albumen, beat the whole 

 into a froth, and, when again liquified, strain through calico. The plates may now 

 be put away to dry ; they are perfectly insensitive to light, and will keep for any 

 length of time. 'When wanted for use, dip them again into the nitrate-bath for 

 one minute, and wash precisely as before. They are now ready for the camera, 

 and may be kept (in darkness of course) for weeks without losing sensitiveness. 

 Develope with pyro-gallic acid, adding free nitrate, if necessary, (this is a long 

 process), and fix with hyposulphite of soda. 



Mr. Hardwich has brought out another edition of his excellent treatise on 

 Photographic chemistry: he now recommends the use of fused nitrate of silver 

 instead of the crystallised. Mr. Scott Archer, the inventor of the Collodion pro- 

 cess has died, leaving a widow and family in distressed circumstances. A com- 

 mittee of the Photographic Society has been formed to raise a subscription for 

 them and to urge their claims on government for pecuniary aid. Mr. Crookes 

 and Mr. Grubb have succeeded in procuring photographic images of the moon — the 

 former with the Liverpool Equatorial obtaining good negatives in four seconds. 

 No practical benefit seems likely to result from this mode of operation, as the 

 minute image thus formed loses its distinctness on being magnified. Is Bromine 

 of any use in Photography ? It seems conceded that in the paper-processes Bro- 

 mine is useful in gainiug intensity ; but in collodion there does not appear to be 

 the same result. For some time it was imagined that the Bromide was peculiarly 

 sensitive to the green rays of the spectrum, and was on this account advantage- 

 ously employed when vegetation and foliage were to be photographed ; but Mr. 

 Crookes has shown that the only part of the spectrum where it enjoys any advan- 

 tage over the Iodide is the unimportant and narrow strip between Fraunhofer's b 

 and G, so that its fancied superiority vanishes compared with the injury it inflicts 

 on the film. Mr. Shadbolt has confirmed by a remarkable experiment the infe- 

 rence of M. Claudet, that the yellow rays not only destroy the actinic effect of the 

 blue, but actually reverse it. Mr. Shadbolt says : " I coated and excited a glass 

 plate in the usual way, and exposed it to the light. I then took a piece of stained 



