396 



NOTES AND QUERIES. 



[No. 156. 



proportion, of the protonltrate of iron to add to 

 the pyroo;allIc solution as a starting-point ? leaving 

 the proportions subsequently to be moditied by 

 the manipulator according to the colour he may 

 wish to give to the picture ? 



4. Query. — When the iron is used, is the pyro' 

 gallic solution still to contain the one drop of 

 nitric acid ? And is the nitric acid always to be 

 used, whether for the production of positives or 

 negatives ? 



G. Query. — Would it not be well to add a little 

 iodide of silver to the saturated solution of hypo- 

 sulphite of soda in the first instance, so that the 

 earliest pictures obtained might have the benefit 

 of it as well as the later ones ? and if so, how much 

 to each ounce of hypo. ? 



It should be held by every one professing to 

 describe delicate processes, that the terms weak 

 solutions, strong solutions, a little of this, and a 

 few lumps of that, should be totally inadmissible. 

 The precise quantity should at all times be named 

 when possible ; and where, as it will sometimes 

 happen, the exact quantity or proportion is diffi- 

 cult to determine under varying circumstances, 

 there is always an approximate quantity which 

 may, and ought to, be given as a starting-point. 

 As when Dr. Diamond says, " It is difficult to 

 determine the exact quantity of this solution (the 

 iodide of silver) which will be required to pro- 

 perly iodize the collodion, probably about ten or 

 twelve drops to every ounce." There is something 

 to go upon. I. W. 



REPLY TO I. W.'S OBSERVATIONS. 



1. All collodion pictures are positives when 

 looked at, and negatives when seen through, and a 

 perfectly good positive will in some instances print 

 as a negative a good positive copy, although in 

 general the development should be overcarried as 

 a positive to produce a strong negative. 



2. If the collodion remains turbid, it is because 

 the iodide of silver is not in a state of solution ; 

 it is rendered soluble by the addition of spirits of 

 wine, which should be as sparingly used as pos- 

 sible : to filter the collodion would mechanically 

 take out the Iodide, and thus the collodion be 

 weak in action. To filter collodion would at all 

 times produce much loss by evaporation. 



Nitrate of potash is not formed in the process 

 which I have described. 



3. Although the protonitrate of iron is to be used 

 when first made, it does not always undergo speedy 

 decomposition. I have used it often when it has 

 been made many weeks. When of an emerald 

 green colour it Is always good, and loses its pro- 

 perties as it assumes a rusty yellow tinge, until It 

 becomes opaque and quite unfit for use. 



4. I think nitric acid iceakens pictures as nega- 

 tives, for it increases the transparency of the deposit, 

 and if I required negatives I would not use it. 



5. The adding the iodide of silver would cer- 

 tainly deprive the hyposulphite of soda of some of 

 its activity, though I believe it would produce a 

 more agreeable tone of picture in the first instance; 

 but a very i'&vr applications sufficiently act upon 

 the hyposulphite as to render this an useless pre- 

 caution. 



Lastly, I quite agree with I. W. upon his 

 strictures of the indefinite terms, weak, strong, a 

 little, afetv lumps, &c. ; but all chemicals, however 

 carefully prepared, constantly vary in their action, 

 and the operator must rely to some extent upon 

 his own judgment, and gain his experience by 

 actually working the processes with his own hands. 

 H. W. D. 



Archer'' s Photographic Camera. — We have re- 

 ceived a letter from Mr. Archer complaining tha4 

 Dr. Diamond, In his communication of the 18th 

 September (see ante, p. 277.), should have attri- 

 buted to Mr. Brown of Ewell the original design 

 of this camera. We were sure that Dr. Diamond 

 had no intention of doing Injustice to Mr. Archer, 

 and therefore referred his communication to that 

 gentleman, who informs us, that although the 

 plan of developing Talbotype pictures in a closed 

 box or camera had been practised by Mr. Archer, 

 such closed box or camera was not applicable to 

 the collodion process until It was modified into its 

 present form by Mr. Brown. Dr. Diamond would 

 therefore gladly amend the passage objected to, 

 by substituting for "as originally designed by Mr. 

 William Bi-own of Ewell," the words " as first 

 suggested by Mr. Archer, and eventually rendered 

 available by Mr. Brown." 



AVe may add, in confirmation of the accuracy of 

 this statement, that we have seen in the posses- 

 sion of Dr. Diamond a view of Merstham Church 

 taken by Mr. Brown, which it is believed is the 

 first perfect collodion picture ever developed In 

 such a camera ; and when the operator was away 

 from home, and relying on the resources which he 

 had with him. 



Black Positive Paper. — I had long been a well- 

 wisher to " N. & Q.," and have been a subscriber 

 from the beginning, but I am more than ever In- 

 terested In it now that you have admitted the 

 subject of Photography In its columns. Can any 

 of your correspondents give me a receipt for a 

 black positive paper ? Some of the French views 

 are of a singularly rich purple black ; how is this 

 effected ? 



Have any of your readers a dark cupboard ? if 

 so, let them be careful not to let the collodion get 

 too near the candle. I had an alarming blow-up 

 the other day through carelessness on this point. 



Nedlam. 



[The rich dark appearance which many of the 

 French photographs possess, is produced from the 

 paper being prepared for what may be called the am- 



