PHOSPHORUS. P=32. This remarkable elementary body is contained in the bones and fluids of animaLs, and also in the vege table and mineral kingdoms. In bones it exists as phosphate of lime, and is obtained from them by acting on calcined bones with sulphuric acid, and distilling the superphosphate of lime thus pro duced with the addition of charcoal. The phosphorus, which is volatile, passes over, and its vapour is condensed and drops into water. It is at first a soft translucent yellowish white substance, but becomes red by exposure to light, which is suppose,d to afford att instance of allotropy. It is insoluble in water, but soluble in oils and in ether.
Phosphonis is highly combustible and burns slowly and spon taneously in the air, but magnificently in oxygen. It should be kept, and cut, under water. Its chief use is for making lucifer matches.
-G LvAzionne.Pmr. This is a process for producing copper plates ready for the printer by the joint action of light and electricity. A company was formed at Holloway, in 1856, for carry ing out the process, under a patent obtained by Herr Pretsch, who superintended operations.
We paid a visit to the establishment in November of that year, and Herr Pretsch WAS kind enough to expla:m the various stages of the process. We subsequently wrote the following article in " Pho tographic Notes." No. 15, describing what we had seen and heard.
" A positive photographic print is first taken,—generally on paper. In order to produce from this a copperplate the following operations are employed :— " First ;—A sheet of glass is coated with gelatine containing bichromate of potass, and other chemicals. When dry, the positive is laid upon it, face upwards, and it is exposed to light in a pressure frame for a few hours. The time of exposure of course depends on the intensity of the light. Sunshine is preferred, but is not necessary. The picture upon the gelatine is developed in raised and sunk parts by immersion in a fluid, the principal constituent of which is water. Where the light has not acted, the gelatine swells and forms a ridge, or a series of minute granulations. Where the light has acted, the gelatine is hardened and does not swell. The picture upon the gelatine is very carious, and resembles a positive by reflected light, the sha dows and dark parts being rough and the lights smooth and polished.
" Second ;—A mould of the picture upon the gelatine is taken in gutta percha. This mould is an intaglio picture, precisely resem bling the finished copper plate. The gutta percha mould is about half an inch thick.
" Third ;—A copper plate is made from the gutta percha mould, by means of the electrotype process. This part of the process is very slow, occupying perhaps a week or two. The copper plate thus ob tained is called the matrix. It precisely resembles the original gelatine picture.
" Fourth ;—The copper plate from which the proof is to be printed is now obtained by the electrotype process from the matrix. This is a slower process than the last, because the copper is much thicker. It occupies about three or four we,eks.
" The entire process therefore occupies about six we,eks. From the final plate four or five hundred good impressions may be struck in the ordinary way ;—a considerable number of plates may be ob tained from the matrix ;—a considerable number of matrices may be taken from the gutta percha mould ;— and a considerable number of gutta percha moulds from the gelatine picture. Here then are the means of almost indefinite multiplication. Some idea of the number of proofs which might be obtained from the original gelatine picture would perhaps be got by multiplying 500 by itself four times. This gives more than sixty thousand million impressions; that is, sufficient proofs for six times the present population of the earth. The most elaborate subjects may be engraved by this process in as short a time as the simplest, the amount of detail in a photograph or photo-galvano graph making no difference, for light, chemistry, and electricity do the work. The time at present required for any subject is a few weeks ; the time frequently spent on engravings is two or three years." The company ceased operations a few months ago, probably from the process not being in a sufficiently perfect state to render them independent of the help of the engraver for retouching their plates. This is much to be regretted, because the process is perfectly suitable for a class of bold artistic subjects which, taken from nature by photo graphy and multiplied in printers' ink, would be of great service as studies for artists, or copies for drawing masters to lay before their Pupils.