Photographic Notes. 171 
The Magnesium Light in Photography. 
Professor Dr. Hermann Cohn, Breslau, is of opinion that the 
“lightning powder” used of late (consisting of magnesium pow- 
dered and chlorate of potash in equal parts) is disadvantageous, 
for the following reasons:—1. On account of the dangerous 
character of this powder it cannot be prepared in large quantities 
and stored for use, but must be carefully prepared for use as 
occasion requires. 2. It is not easy to set on fire at the precise 
moment desired, even with the electric spark. Fuming sulphuric 
acid will do this, Dr. Cohn has been told, but this is not a desir- 
able substance to deal with, as its vapour would damage any delicate 
apparatus in the vicinity. 3. It is not always desirable to have a 
double illumination. 4. The light should be “ photochemical.” 
Professor Cohn obviates all these inconveniences by using simple 
magnesium powder, which is then blown through any flame in use 
by means of a simple little apparatus (which may be obtained for 
3s. from Herr Pusch, Breslau, Schmiedebriicke 46). Armed with 
this and a small benzine lamp, anyone can produce a momentary 
and brilliant illumination, and with this may obtain photographs 
anywhere and at any time. Magnesium is only about 2d. a grain, 
and a grain or two amply suffices. For medical photographers 
nothing can be simpler than Professor Cohn’s magnesium benzine 
light.— British Medical Journal. 
Photographic Notes. 
Etching upon Boxwood Blocks,—Photographic etching upon 
box-wood blocks, such as are used in wood-engraving, has been 
deemed a practical impossibility. We learn, however, that it has 
recently been accomplished in Russia, and by a method simple and 
ingenious. The block in its natural condition is, of course, 
unsuitable. The first step is to fill the pores with insoluble car- 
bonate of copper, by means of two separate solutions, in which it 
is boiled sufficiently. A polish is then imparted to its surface, 
asphalt in solution applied to its back and sides, and finally a 
sensitised gelatine film placed over the polished face. 
The subject to be etched is now photographed on the surface, 
and, by washing, the soluble and unprinted parts of the gelatine 
removed. A coating of asphalt is next applied to the raised parts, 
the blocks steeped in nitric acid of suitable strength (the stronger 
the better), where it remains one hour, when it is removed and 
subjected to the action of sulphuric acid for the same time. The 
