170 W. Crookes on the Wax-paper Photographic Process. 



produce a somewhat similar effect to that of a bromid, but in a 

 less marked degree. As no particular advantage could be traced 

 to it, it was not employed. 



35. I have also tried most of the different forms of organic 

 matter, which it is customary to add to this bath, but I cannot 

 recommend them ; the most that can be said is, that some of 

 them do no harm. At first I thought a little isinglass might be 

 an improvement, as it instantly removes the greasiness from the 

 surface of the paper, and allows the iodid of potassiutn to pene- 

 trate more readily. Unfortunately, however, it interferes with 

 the most important property of this process, that of remaining 

 sensitive for a long time. 



36. I think the best results are obtained, when the iodid and 

 bromid are mixed in the proportion of their atomic weights ; the 

 strength being as follows: 



Iodid of potassium . . . 582 '5 grains, 

 Bromid of potassium . . 417'5 grains. 

 Distilled water .... 4(i ounces.* 



When the two salts have dissolved in the water, the mixture 

 should be filtered ; the bath will then be fit for use. 



37. At first, a slight difficulty will be felt in immersing the 

 waxed sheets in the liquid without enclosing air bubbles, the 

 greasy nature of the surface causing the solution to run off. 

 The best way is to hold the paper by one end, and gradually to 

 bring it down on to the liquid, commencing at the other end ; 

 the paper ought not to slant towards the surface of the bath, or 

 there will be danger of enclosing air bubbles ; but while it is 

 being laid down, the part out of the liquid should be kept as 

 nearly as possible perpendicular to the surface of the liquid ; any 

 curling up of the sheet when first laid down, may be prevented 

 by breathing on it gently. In about ten minutes, the sheet 

 ought to be lifted up by one corner, and turned over in the same 

 manner; a slight agitation of the dish will then throw the liquid 

 entirely over that sheet, and another can be treated in like 

 manner. 



38. The sheets must remain soaking in this bath for about 

 three hours; several times during that interval, (and especially 

 if there be many sheets in the same bath,) they ought to be 

 moved about and turned over singly, to allow of the liquid pen- 

 etrating between them, and coming perfectly in contact with 

 every part of the surface. After they have soaked for a suffi- 

 cient time, the sheets should be taken out and hung up to dry; 

 this is conveniently affected by stretching a string across the 



* While giving the above as the calculated quantities, I do not wish to insist 

 upon their being adhered to with any extreme accuracy. An error of a few grains 

 on either side would I believe be without any perceptible effect on the result. 



