160 APPENDIX. [No. IV. 



a very excellent paper may be made by a solution containing ten grains 

 of salt and twelve of chloride of lime to the ounce of water. 



Dilute muriatic acid may also be used for tbe manufacture of tbe 

 photogenic paper, in tbe proportion of about twenty-four drops of tie 

 distilled acid, sp. gi\ 1-12, to an ounce of water. It may be used either on 

 the glazed or absorbent papers, but for the latter it should not exceed half 

 the strength. The same observations apply to any excess of muriatic acid 

 as were noticed to, apply to the fluoride of sodium. This forms a delicate 

 paper, and becomes of a very even colour. 



A more sensitive paper may be prepared by using the bromide of 

 silver instead of the chloride ; but the expense of bromine and its com- 

 pounds is an objection. 



A solution of bromine in water cannot be used in a way similar to a 

 solution of chlorine with any good result, and recourse must be had to the 

 bromide of potassium, of which twelve grains to the ounce, applied in the way 

 described when treating of the chloride of silver, and afterwards conjoined 

 with a solution of nitrate of silver (fifty grains to the ounce), will be found 

 a suitable proportion. 



Other salts may be used besides the chloride and bromide, such as the 

 phosphates, chlorates, &c., but have the disadvantage of not being so 

 sensitive to light. A benefit, however, attends the use of the phosphates, 

 &c. ; for while any excess of the chlorides must be carefully avoided, an 

 undue proportion of the latter salts is attended with no inconvenience. 



The expense of the nitrate of silver renders it desirable to reduce the 

 quantity used ; but if a dart ground is wanted, a smaller quantity than 

 fifty grains to the ounce cannot well be employed. 



Having considered the chemical substances which may be used for 

 the photogenic paper, the different kinds of paper, and those suited to 

 each particular preparation of silver, next demand attention. 



Papers may be divided into three classes — the bibulous, the absorbent, 

 and the highly-glazed papers. Of the bibulous papers, blotting-paper 

 and tissue papers are examples ; but none of them will be found at all 

 applicable to the purposes of the photogenic art. These papers are made 

 from rags, but there are papers made from other substances, such as old 

 sacking, &c., which possess great strength, as well after they have been 

 moistened as before. 



The finest paper of this sort is caUed "double small ends." That 

 which I employed, when sponged over, seemed to be equally moistened 

 in eveiy part, and was found well adapted for the intended purpose, as 

 there was not, after being prepared with the solutions, a single spot that 

 resisted the action of light in any one of the sheets. There are, however, 

 disadvantages attending the use of this paper, for it is not so smooth as 

 others more highly glazed, and therefore not so weU adapted for every 

 description of photographs. 



The absorbent papers, or the papers used in printing, possess a finer 

 texture than that last described ; and when they can be obtained good, 

 they answer very well for photogenic purposes. 



Of the various papers which have been tried of this description, a 

 thin paper used for printing newspapers, called " double copy," was found 

 the best j for the thicker papers, that have much plaster of Paris added 

 to increase their substance and weight, do not answer so well, as they 



