ON SELF-RECORDING MAGNETOGRAPHS. 209 



11. The vessel in which the wax is melted, must be contrived so as never 

 to allow of its reaching a higher temperature than 212° Fahr., or decompo- 

 sition of the wax might ensue. 1 have found the most convenient apparatus 

 to be, a tin vessel 15 inches square and 4 inches deep, having a tray which 

 holds the wax fitting into it about 1 inch deep. The under vessel is to be 

 half filled with water, and by keeping this just at the boiling temperature, the 

 wax above will soon become liquid. 



12. The best source of heat is that known as the gauze gas-burner, it 

 being free from smoke or dust, and not liable to blacken anything placed 

 over it. It consists of a common argand burner fixed on a rather low and 

 heavy iron stand, which is surmounted by a copper or brass cylinder 5 inches 

 in height and 2 inches wide, having a piece of wire gauze of 900 meshes to 

 the square inch fastened over the top. By connecting this burner by means 

 of vulcanized india-rubber tubing to the gas-pipe, it can be moved about 

 the table to any convenient position. The mixture of gas and air, formed 

 inside the cylinder, is to be lighted above the wire gauze ; it burns over this 

 with a large and nearly colourless but intensely hot flame. 



13. The most convenient form of iron is the ordinary box iron, made 

 hot by heaters inside ; perhaps it might be improved in shape by having 

 the end not quite so pointed, but this is not of much consequence. Some 

 operators recommend facing the bottom with a plate of silver ; this is very 

 expensive, and seems to me to be attended with no advantage whatever. 



14. For the purpose of absorbing the excess of wax from the surface of 

 the sheet, I should recommend the ordinary white wove blotting-paper, 

 medium thickness. But this is not sufficiently free from impurities to serve 

 either for drying the sensitive sheets, or for filtering ; for this purpose, the 

 fine filtering paper (not the Swedish) employed in quantitative chemical 

 operations is the best. 



15. The distilled water being one of those substances upon the purity 

 of which success will in a great measure depend, it will be found much safer 

 to distil it on the premises, especially as the quantity required is trifling. 

 A convenient size for the still is about two gallons; it may be procured 

 ready made, with worm, &c. complete, of any large dealer in chemical 

 apparatus. It will be found far more economical, both in time and trouble, 

 to heat the water over a charcoal or coke fire, in preference to using gas 

 for this purpose. 



16. A platinum spatula is a most necessary instrument in almost every 

 operation ; the best size is 4 inches long, % an inch wide at one end, and -| at 

 the other, the corners being rounded off; it should be of a sufficient sub- 

 stance to prevent its being easily bent. It chief use is to raise one corner 

 of the sheets to allow of their being held between the finger and thumb, for 

 the purpose of removing from one dish to another, as, previous to fixing, 

 none of the solutions should come in contact with the fingers. 



During the fixing and subsequent washing, bone spatulas will be found 

 very useful ; but after having been in contact with hyposulphite of soda, 

 they must be carefully kept away from any of the previous baths, or black 

 stains will infallibly ensue. 



17. The funnels may be either of glass or porcelain ; it will be found 

 useful to have several of different sizes, from 2 inches diameter, up to 6 

 inches. A convenient stand for them may be made of a piece of flat board, 

 with circular holes, about half the diameter of the funnels employed, drilled 

 into it, and supported upon four legs about 8 inches high. The paper 

 used for filtering should be the finest of the two sorts of blotting-paper 

 mentioned above (14). The filters can either be cut from the sheet as 

 wanted, or they may be obtained ready cut in packets. 



1859. P 



