158 



NOTES AND QUERIES. 



[No. 225. 



silver to the double iodide, as recommended by Dr. 

 Diamond. I tried this, and feel most confident that it 

 produces no difference ; as soon as the bromide of 

 silver comes in contact with the iodide of potassium, 

 double decomposition ensues, and iodide of silver is 

 formed. Indeed, farther, this very double decompo- 

 sition, or a similar one, is the basis of a patent I have 

 just taken for at the same time refining silver and ma- 

 nufacturing iodide of potassium ; a process by which I 

 much hope the enormous present price of iodide of 

 potassium will be much lowered. F. Maxwell Ltte. 

 Hotel de l'Europe, 

 a Pau, Basses Pyrenees. 



P. S. — Since writing the former part of this letter, I 

 see in La Lumiire a paper on the subject of printing 

 positives, in part of which the addition of nitric acid is 

 recommended to the bath ; but as my experiments have 

 been quite independent of theirs, and my process one 

 of a different nature, I still send it to you. When 1 

 have an opportunity, I will send a couple of specimens 

 °f m y workmanship. I had prepared some for the 

 Exhibition, but could not get them off in time. I may 

 add that the developing agent I use is the same in 

 every way as that I have before indicated through the 

 medium of your pages ; but where formic acid cannot 

 be got, the best developer is made as follows : 



Pyrogallic acid - - - -27 grs. 



Acetic acid - - . - 6 drs. 



Water - - -, - - 9 oz. 



On Sensitive Collodion. — As I have lately received 

 many requests from friends upon the subject of the 

 most sensitive collodion, I am induced to send you a 

 few words upon it. 



Since my former communication, I believe a greater 

 certainty of manufacture has been attained, whereby 

 the operator may more safely rely upon uniformity of 

 success. 



I have not only tried every purchasable collodion, 

 but my experiments have been innumerable, especially 

 in respect to the ammoniated salts, and I may, I think, 

 safely affirm that all preparations containing ammonia 

 ought to be rejected. Often, certainly, great rapidity 

 of action is obtained ; but that collodion which acted 

 so well on one day may, on the following, become 

 comparatively useless, from the change which appears 

 so frequently to take place in the ammoniacal com- 

 pounds. That blackening and fogging, of which so 

 much has been said, I much think is one of the results 

 of ammonia ; but not having, in my own manipula- 

 tions, met with the difficulty, I have little personal 

 experience upon the subject. 



The more simple a collodion is the better ; and the 

 following, from its little varying and active qualities, I 

 believe to be equal to any now in use. 



A great deal has also been said upon the preparation 

 of the simple collodion, and that some samples, however 

 good apparently, never sensitize in a satisfactory man- 

 ner. I have not experienced this difficulty myself, or 

 any appreciable variation. 



The collodion made from the Swedish filtering 

 paper, or the papier Joseph, is preferable, from the 

 much greater care with which it is used. 



If slips of either of these papers be carefully and 

 completely immersed for four hours in a mixture of an 

 equal part (by weight) of strong nitric acid or nitrous 

 acid (the aqua fortis of commerce) and strong sulphuric 

 acid, then perfectly washed, so as to get entirely rid of 

 the acids, the result will be an entirely soluble mate- 

 rial. About 100 grains of dry paper to a pint (twenty 

 ounces) of ether will form a collodion of the desired 

 consistence for photographic purposes. If too thick, it 

 may be reduced by pure ether or alcohol. However 

 carefully this soluble paper or the gun cotton is pre- 

 pared, it is liable to decompose even when kept with 

 care. I would therefore advise it to be mixed with 

 the ether soon after preparation, as the simple collodion 

 keeps exceedingly well. Excellent simple collodion is 

 to be procured now at the reasonable price of eight 

 shillings the pint, which will to many be more satis- 

 factory than trusting to their own operations. 



To make the sensitizing Fluid. — Put into a clean 

 stoppered bottle, holding more than the quantity re- 

 quired so as to allow of free shaking, six drachms of 

 iodide of potassium and one drachm of bromide of 

 potassium ; wet them with one drachm of distilled 

 water first, then pour into the bottle ten ounces of 

 spirits of wine (not alcohol) ; shake frequently until 

 dissolved. After some hours, if the solution has not 

 taken place, add a few more drops of water, the salts 

 being highly soluble in water, though sparingly so in 

 rectified spirits ; but care must be taken not to add too 

 much, as it prevents the subsequent adhesion of the col- 

 lodion film to the glass. 



A drachm and a half to two drachms, according to 

 the degree of intensity desired, added to the ounce of 

 the above collodion, which should have remained a few 

 days to settle before sensitizing, I find to act most sa- 

 tisfactorily ; in fine weather it is instantaneous, being, 

 after a good shake, fit for immediate use. If the sensi- 

 tive collodion soon assumes a reddish colour, it is im- 

 proved by the addition of one or two drops of a satu- 

 rated solution of cyanide of potassium ; but great care 

 must be used, as this salt is very active. 



Hugh W. Diamond. 



ftfjiltesi to Minax Qnrrief, 



Portrait of Alva (Vol. ix., p. 76.). — There is 

 a fine portrait of the Duke of Alva in the Royal 

 Museum at Amsterdam, by D. Barendz (No. 14. 

 in the Catalogue of 1848) ; and Mr. Warden will 

 find a spirited etching of him, decorated with the 

 Order of the Golden Fleece, in the Historia Bel- 

 gica of Meteranus (folio, 1597), at p. 63. The 

 latter portrait is very Quixotic in aspect at the 

 first glance, but the expression becomes more 

 Satanic as the eye rests on it. Lancastriensis. 



Lord Mayor of London not a Privy Councillor 

 (Vol. iv. passim; Vol. ix., p. 137.). — L. Hartly 

 a little misstates Mr. Serjeant Merewether's evi- 

 dence. The learned Serjeant only said that "he 

 believed " the fact was so. But he was un- 

 doubtedly mistaken, probably from confounding 



