178 On a new Accelerating Process in Photography. 



cannot be inferred by the rule : — Compute the grains of lime, 

 magnesia, oxides of iron, alumina, in a gallon of water, each 

 into its equivalent of chalk: the sum of these equivalents will 

 be the hardness of the water. 



3rd. That the degrees of hardness of a water containing 

 magnesia and lime salts, as shown by the soap-test as it is now 

 applied, cannot in almost every case be taken as representing 

 the amount of these salts in the water ; nor in nearly every 

 instance can it be considered as giving the amount of lime in 

 a water when magnesia is present. 



4th. That water might show by the soap-test a small de- 

 gree of hardness in comparison to the considerable quantities 

 of salts of magnesia and of lime it might contain, and trusting 

 to this method of analysis alone when selecting water for 

 ordinary use and for steam purposes, might lead to a water 

 being selected which might not be conducive to the general 

 health, and which would leave considerable deposit in vessels 

 in which it was boiled, — a great deterioration to its use in 

 steam generating. 



XXI. On an Accelerating Process in Photography. 

 By J. Middleton, F.G.S.* 



THE following method of preparing sensitive paper, may, 

 perhaps, be welcome to photographers on account of the 

 great sensibility which it confers ; it has the additional recom- 

 mendation, moreover, of being very simple and constant in its 

 results. 



I beat up albumen of the e^g of the duck till it becomes 

 liquid, and then mix it with water in the proportion of eighty 

 grains of the former to an ounce of the latter. I add to this 

 solution iodide of potassium in the proportion of twenty-five 

 grains to the ounce. Prior to the application of this solution 

 I wash the size from the side to be rendered sensitive, by 

 means of a camel-hair brush, and when dry I float the paper 

 on the solution, for from three to four minutes, and when 

 drained and dried I lay it aside for use. 



When about to be used for taking a picture, the paper, 

 prepared as above directed, is to be washed with aceto-nitrate 

 of silver, in the proportion of sixty grains of nitrate and 

 eighty grains of acetic acid to an ounce of water (Talbot's 

 strength). I apply the solution with a glass rod, in the 

 manner recommended some time since by a writer in the 

 Philosophical Magazine, using about forty grains of it to a 



* Communicated by the Author. 



