212 report — 1859. 



Weigh out accurately 10 grains of nitrate of silver, dissolve this in half an 

 ounce of distilled water; then add 4< grains of chloride of sodium (common 

 salt), also dissolved in water. On mixing these two solutions together, a 

 white curdy precipitate of chloride of silver will fall down. Next add 22 

 grains of the hyposulphite of soda, and allow it to stand for about ten 

 minutes, stirring occasionally with a glass rod. If at the end of that time 

 the chloride of silver has dissolved, the hyposulphite of soda may be con- 

 sidered as pure. A greater or less amount of residue will indicate roughly 

 the degree of impurity. 



26. The cyanide of potassium is usually met with in the form of hard 

 white lumps; they will be found quite pure enough. It is very useful in 

 removing stains formed by nitrate of silver on the fingers, &c. ; but the 

 greatest care must be taken in its employment, as it is a most energetic poison; 

 its use in cleaning the dishes from silver stains has been pointed out above 

 (10). 



27. The first operation to be performed is to make a slight pencil mark on 

 that side of the photographic paper which is to receive the sensitive coating. 

 If a sheet of Canson's paper be examined in a good light, one of the sides 

 will be found to present a finely reticulated appearance, while the other will 

 be perfectly smooth ; this latter is the one that should be marked. Fifty or 

 a hundred sheets may be marked at once, by holding a pile of them firmly 

 by one end, and then bending the packet round, until the loose ends separate 

 one from another like a fan ; generally all the sheets lie in the same direc- 

 tion, therefore it is only necessary to ascertain that the smooth side of one of 

 them is uppermost, and then draw a pencil once or twice along the exposed 

 edges. 



28. The paper has now to be saturated with white wax. The apparatus 

 for this purpose has been previously described (11)- The wax is to be 

 made perfectly liquid, and then the sheets of paper, taken up singly and 

 held by one end, are gradually lowered on to the fluid. As soon as the wax 

 is absorbed, which takes place almost directly, they are to be lifted up with 

 rather a quick movement, held by one corner and allowed to drain until the 

 wax, ceasing to run off, congeals on the surface. When the sheets are first 

 taken up for this operation, they should be briefly examined, and such as 

 show the water- mark, contain any black spots*, or have anything unusual 

 about their appearance, should be rejected. 



29. The paper in this stage will contain far more wax than necessary; the 

 excess may be removed by placing the sheets singly between blotting-paper 

 (14), and ironing them; but this is wasteful, and the loss may be avoided 

 by placing on each side of the waxed sheet two or three sheets of unwaxed 

 photographic paper, and then ironing the whole between blotting-paper; 

 there will generally be enough wax on the centre sheet to saturate fully those 

 next to it on each side, and partially, if not entirely, the others. Those that 

 are imperfectly waxed may be made the outer sheets of the succeeding set. 

 Finally, each sheet must be separately ironed between blotting-paper until 

 the glistening patches of wax are absorbed. 



30. It is of the utmost consequence that the temperature of the iron should 

 not exceed that of boiling water. Before using, I always dip it into water 

 until (he hissing entirely ceases. This is one of the most important points in 

 the whole process, but one which it is very difficult to make beginners pro- 

 perly appreciate. The disadvantages of having too hot an iron, are not 



* These spots have been analysed by Mr. Malone ; he finds them to consist, not of iron, 

 as is generally supposed, but of small pieces of brass. I have also examined them myself 

 with a like result. 



