326 



KNO\A/LEDGE 



[April 17, 1885. 



marked " soil-pipe " in the figure, does not permit of any 

 lodgment for sewer-gas, and there cannot be any risk of 

 the water in the trap being syphoned out. There are thus 

 no untrapped joints within the buikiing, whilst the mate- 

 rial out of which it is made prevents any injury through 

 decay. It can be adapted to any existing form of appa- 

 ratus, and absolutely prevents the entry of sewer-gas into 

 the house through the closet apparatus. 



SIMPLE METHODS OF MAKING 



LANTERN-SLIDES. 

 By W. Jerome Harrison, F.G.S. 



(Continued from pafjc 285.) 

 PRODUCTION OF LANTERN-SLIDES BY PHOTOGRAPHY. 



OF all methods for the production of lantern-slides 

 photography is by far the most satisfactory, and the 

 reason is not far to seek. When a picture which has been 

 drawn or painted by hand is greatly magnified the defects 

 stand out glaringly. I am in the habit of using a 22-ft. 

 screen, but when the picture exceeds 8 or 10 ft. in 

 diameter I only venture to employ first-rate photographs, 

 taken direct from natural objects. The "lights" of the 

 picture shouhl be represented on the slide by absolutely 

 clear glass, and there should be a gradation of tints from 

 this to nearly but not quite opaque portions, but of the 

 latter there should be but little. It is this variation in 

 the thickness of the colouring matter which gives the 

 " sparkle " to a good photograph. 



The Gelatino-Ohloride Process. — "We need not go 

 into the details by which the " dry " plates to be employed 

 are made. Suffice it to say that, by a series of chemical 

 changes, we obtain chloride of silver sjiread, in the finest 

 possible particles, throughout a mass of liquid gelatine. 

 A little of this " emulsion " is then poured upon a glass 

 plate, and, being allowed to dry, forms upon it a horny, 

 whitish film, which is extremely sensitive to light — espe- 

 pecially that of the blue end of the spectrum. Obviously, 

 the work of making the emulsion and coating the plates 

 must be conducted in red or yellow light only ; and so, too, 

 must all the subxeqiient operations until the slide bears the 

 finished picture. For this reason we generally conduct the 

 slide-making by night, or in a darkened room, using a 

 lantern glazed with ruby glass. The ai)paratus required is 

 as follows : — (1) Printing- frame (cost 6d. to Is.) ; (2) magne- 

 sium ribbon (3d. per foot), cut into pieces one inch long ; 

 (3) two ihallov} diahes, of glass or ebonite (cost about 

 Is. 6d. each for small sizes), a little larger than the glass 

 negatives from which the slides are to be copied ; (1) the 

 following chemicals : citric acid, 2 oz. ; carbonate of am- 

 monia, 2 oz. ; sulphate of iron, 4 oz. ; sulphuric acid, I lb. ; 

 and hyposulphite of soda, 2 lb. ; (5) the gelatino- chloride 

 plates (those I have used are prepared by Mr. Cowan, 

 and sold by Marion & Co., Soho-square). Their price is 

 2s. per dozen for lantern size; but they may be had in 

 various sizes, up to one foot square, and the large plates 

 give lovely eff-'cta by transmitted light ; (C) a broad, iiat 

 camel-hair brush (cost 5d.) 



Manipulation. — Place the negative, film side upwards, 

 in a piinting-frame, and lay the sensitive gelatino-chloride 

 plate upon it, in close contact, film touching film. Now 

 put on the wooden back of the frame and close the springs, 

 thus pressing the two glass plates firmly and securely 

 together. 



Next lay a 2-ft. rule upon a table, and place the printing- 

 frame upright at one end of the rule. Take an inch-length 



of magnesium ribbon in a pair of forceps, ignite by means 

 of a match, and hold it at the other end of the rule, so that 

 the light falls upon the outer glass surface of the negative 

 in the printing-frame. The result will be a change in the 

 chloride of silver on the plate beneath, by which all the 

 details of the picture will be reproduced upon the gelatino- 

 chloride plate. 



Remove the latter from the frame, and examine it by the 

 red light of the lamp. The surface appears unchanged. 

 The positive picture is there, but it is so feeble that it 

 cannot be seen. To strengthen the image and render it 

 vii-ible, the plate requires to be developed. For this purpose, 

 make up the following solutions : — 



I. Citric acid 120 gra. 



Cai'bonate of ammonia 88 gra. 



Di.stilled water (cold) 1 oz. 



II. Sulphate of iron 140 gra. 



Sulphuric acid 1 drop. 



Distilled water 1 oz. 



III. Common salt 1 oz. 



Water 10 oz. 



Solutions Nos. I. and II. must be mixed in the propor- 

 tions of one part of No. II. to three parts of No. I. 

 Always pour No. I. into the measuring glass first, and then 

 add the sulphate of iron solution to it. For a plate of the 

 regulation size (3| in. square), half an ounce of No. II. may 

 be added to Ih oz. of No. I. Further, to every ounce of 

 the mixture add five drops of the salt solution (No. III.) 



All being ready, place the chloride-plate — film upwards 

 — in one of the shallow dishes, and cover it with water. 

 Pour away the water, and pour on the developing mixture, 

 prepared as above ; now use the camel-hair brush, passing 

 it backwards and forwards three or four times over the 

 surface of the plate, so as to remove any air-bubbles. 



Watch the surface of the plate carefully, using a card- 

 board cover to screen the dish as much as possible, even 

 from the red light in which all this work must be done. 

 Soon the details of the picture will begin to appear, and, 

 after a minute has elapsed, the plate may be lifted from 

 the dish and held between the eye and the red light. If 

 t^g picture is now perfectly distinct and fairly dense it is 

 finished ; but if not, return it to the dish for a minute or 

 two more. 



Now that the development of the picture is completed it 

 must be fixed — that is, the chloride of silver not acted 

 upon by the light ncust be removed. Rinse the plate well 

 under a tap, place it in the second dish, and pour upon it 

 a solution of " hypo " (as the hyposulphite of soda is 

 familiarly termed), made by dissolving four ounces of hypo 

 in twenty ounces of water. Allow the plate to remain in 

 the hypo for five minutes, then remove it, and wash it 

 thoroughly for several hours in a stream of running water, 

 by placing it upright in a basin of water into which a tap 

 is allowed to run. The object of this is to remove every 

 trace of the hypo, which would otherwise speedily destroy 

 the picture. After the washing is completed stand the 

 plate on edge to dry — a process which will probably require 

 several hours. 



Lastly, the picture must be monnted, or its surface will 

 soon sutler from scratches, &,c. First varnish it with the 

 " negati^•e varnish " sold at the photographic warehouses ; 

 then place a cover of clear glass of the same size as the 

 slide upon the picture, and bind the two together with 

 strips of any thin, tough paper (blue " needle-paper " is the 

 best) which has been previously coated with strong gum 

 and alloired to dry. Freshly-gummed paper does not adhere 

 well to glass. If the original negative be a good one, and 

 the manipulations described above are faithfully carried 

 out, an excellent lantern-slide will be obtained. 



