April 16. 1853.] 



NOTES AND QUERIES. 



389 



I find that the plate is more sensitive also, if not 

 exposed before all the exciting fluid that can be 

 drained off is got rid of; that is, while still quite 

 moist, but without any flowing liquid. 



As to redipping the plate before development, 

 it is, I believe, in general useless ; but when the 

 plate has got very dry it may be dipped again, but 

 should be then well drained before the developing 

 solution is applied. 



Mr. F. Maxwell Ltte (p. 364.) quotes the 

 pi-ice of the purest iodide of potassium at Is. Zd. 

 per oz. I should be glad to know where it can be 

 obtained, as I find the price constantly varies, and 

 upon the last occasion I paid 4s. per oz., and I 

 think never less than la. Bd. 



Mr. L. Merritt will probably succeed in ap- 

 plying the cement for a glass bath thus : — Place 

 the pieces of glass upon wood of any kind in an 

 oven with the door open until he can only just 

 handle them ; then, with a roll of the cement, 

 melting the end in the flame of a spirit-lamp, 

 fipply it as if for sealing a letter. This should be 

 done as quickly as possible. The glasses may then 

 be passed over the flame of the lamp (in contact 

 with it), so as to raise the tempei'ature, until 

 the cement is quite soft and nearly boiling (this 

 can be done without heating the parts near the 

 fingers) ; and while hot the two separate pieces 

 should be applied by putting one down on a piece 

 of wood covered with flannel, and pressing the 

 other with any wooden instrument : metal in con- 

 tact would cause an instantaneous fracture. 



Mr. Merritt's difficulty with the developing 

 solutions depends most probably in the case of 

 the pyrogallic acid mixture not having enough 

 acetic acid. The protonitrate of iron, if made 

 according to Dr. Diamond's formula, does not re- 

 quire any acetic acid, and flows quite readily ; 

 but the protosulphate solution requires a bath, 

 and the same solution may be used over and over 

 again. Geo. Shadbolt. 



London, April 9, 185.3. 



Economical Iodizing Process. — Mr. Maxwell 

 Lyte Is probably as good a judge as myself, as to 

 where any weak point or difficulty is found in 

 iodizing paper with the carbonate of potass : if 

 any cliemical is likely to be the cause of unusual 

 activity, it is the carbonic acid, and not the cyanide 

 of potash. I still continue to use that formula, 

 and have not iodized paper with any other : though 

 I have made some variations which may perhaps 

 be of use. I found that the nitrate of potash is 

 almost the same in its effects as the carbonate. 

 I would as soon use the one as the other; but 

 the state I conceive to be the most effective, is 

 the diluted liquor potassse : that would be with 

 iodine about the same state as the iodide of 

 potash, but hitherto I have not tried it, though 

 I mean to do so. 



I am not quite certain as to whether, theoreti- 

 cally, this position is right ; but I find in iodide of 

 potash, and in the above formula, that the iodine 

 is absorbed in greater quantities by the silver, 

 than the alkaline potash by the nitric acid. Thus, 

 by using a solution for some time, it will at last 

 contain but very little iodine at all, and not 

 enough for the purpose of the photographer ; hence 

 it requires renewing. And I have lately observed 

 that paper is much more effective, in every way, 

 if it is floated on free iodine twice before it is used 

 in the camera, viz. once when it is made, and again 

 when it is dry : the last time containing a little 

 bromine water and glacial acetic acid. It appears 

 to me that the paper will absorb its proper dose of 

 iodine better when dry, and the glacial acetic acid 

 will set free any small amount of alkaline potash 

 there may be on the surface ; so that it will not 

 embrown on applying gallic acid. By using the 

 ammonio-nitrate of silver in iodizing, and proceed- 

 ing as above, I find it all I can wish as far as 

 regards the power of my camera. With this paper 

 I can use an aperture of half an inch diameter, 

 and take anything in the shade and open air in 

 five or six minutes, in the sun in less time. The 

 yellow*colour also comes off better in the hypo, 

 sulph. 



I think Mr. Maxwell Ltte has made a mis- 

 take as to the price he quotes : about here I can- 

 not get any iodide of potash under 2s. per ounce, 

 and the five grains to the ounce added to the 

 common dose of nitrate of silver is hardly worth 

 speaking of; it would amount, in fact, to about 

 fifteen grains in a quire of Whatman's paper, — no 

 great hardship, because many use much higher 

 doses of silver for iodizing ; forty grains to the 

 ounce is not uncommonly used, but I believe 

 twenty-five grains quite enough. 



I presume, in Sir Wm. Newton's mode of 

 treating positives, the acid of the alum decomposes 

 the alkali of the hypo, sulph. And It would be, 

 I suppose, better for the picture, If Its state were 

 entirely neutral when put away or framed ; but If 

 alum is added, acid must remain, since Sir Wm. 

 says it combines with the size. What I should 

 imagine is, that the Idea is good ; but experience 

 can only decide if the picture Is better put away 

 in an acid condition. I should think there are 

 more available acids for the purpose, for alum has 

 an Injurious effect upon colour ; and a positive is 

 nothing but colour, the organic matter of the 

 paper stained as it were by the silver : for, after 

 all its washings and application of re-agents, no 

 silver can possibly remain in the paper. The 

 safest state therefore of putting away ought to be 

 ascertained and decided upon ; as it is no use 

 doing them if they fade, or even lose their tones. 



Weld Tayloh. 



N. B. — The iodized ammonio-nitrate paper will 

 not bear exposure to the sun ; it will keep any 



