182 



NOTES AND QUERIES. 



[No. 226. 



it, should they contain any, by fusing them in a por- 

 celain crucible over a spirit-lamp. The ordinary fused 

 lunar caustic of the surgeon is unfit for general use as 

 a photographic agent. J. Leachman. 



Professor Hunt's Photographic Studies. — My atten- 

 tion has just been directed to a " Practical Photo 

 graphic Query" in your Journal, Vol. ix., p. 41., which 

 appears to require a reply from me. It is quite evi- 

 dent that your correspondent, notwithstanding the 

 personal respect which he professes to entertain, cannot 

 have any intimate knowledge of either my works or 

 my studies. Allow me to make my position clear to 

 him and other of your readers. My first photographic 

 experiment dates from January 28, 1839, and since 

 that period the investigation of the chemical plienomena 

 of the solar rays has been the constant employment of 

 all the leisure which a busy life has afforded me. The 

 production of photographic pictures has never been the 

 ultimate object at which I have aimed, although my 

 researches have caused me to obtain thousands. My 

 object has been, and is, to endeavour to obtain some 

 light into the mysteries of the radiant force with which 

 the photographic artist works, being quite content to 

 leave the production of beautiful images to other ma- 

 nipulators. 



As I write on the subject, it appears, of course, ne- 

 cessary that I should be familiar with all the details of 

 manipulation in each process which I may describe. 

 Whenever I have mentioned, in either of my works, a 

 process with which I have not been entirely familiar, 

 I have given the name of the authority upon whom I 

 have depended. But there will not be found in either 

 my Photography, or my Researches on Light (of which 

 a greatly enlarged edition will soon be submitted to 

 the public), any one process upon which 1 have not 

 made such experiments as appeared to me necessary 

 to my understanding the rationale of the chemical 

 changes involved, and of the physical phenomena 

 which arise. 



Now, since it is not necessary to select a picturesque 

 object to instruct me in these points, the same build- 

 ings, trees, and plaster casts have been copied times 

 beyond number; and when the problem under exa- 

 mination has been solved, these pictures have been 

 destroyed. 



There are twenty exhibitors of pictures in the Pho- 

 tographic Gallery who would certainly leave my pro- 

 ductions far behind, as it concerns their pictorial cha- 

 racter ; but I am confident there is not one who has 

 made the philosophy of Photography so entirely his 

 study as I have done. 



I have been engaged for the last two years in study- 

 ing the chemical action of the prismatic spectrum. I 

 inclose you my report on this subject to the British 

 Association for 1852 (that for 1853 is now in the 

 hands of the printer), from which you will perceive 

 that I am employing myself to greater advantage to 

 photography, as a science under art, than I should be 

 did I enter the lists with those who catch the beauties 

 of external nature on their sensitive tablets, and secure 

 for themselves and others pictures drawn by the solar 

 pencil, in which no one can more deeply delight than 

 your humble servant. Robert Hunt. 



Waxed-paper Pictures. — Will your correspondents 

 or yourself do me the favour to say, how such beau- 

 tiful pictures have been produced and exhibited by 

 Mr. Fenton and others by the waxed-paper medium, 

 if that process be so bad and defective ? When I have 

 followed it, and exercised consistent patience, I have 

 ever produced pleasing and faithful results. That 

 when parties do not themselves prepare, it becomes 

 expensive, I am willing to admit; but I am inclined to 

 attribute many failures to the uncertain heat of hot 

 irons, which must vary; and I make this fact known to 

 you as the result of my own observation on many 

 sheets : added to which, defective manipulation, or 

 impure chemicals, must not be allowed to do away 

 with its having much merit. Harley Lane. 



The Double Iodide Solution. — In a note appended 

 to Dr. Mansell's communication on the calotype 

 (Vol. ix., p. 134.), you state that having lately pre- 

 pared the double iodide solution according to the for- 

 mula given by Dr. Diamond, in which it required 

 650 grains of iodide of potassium to dissolve a 60-grain 

 precipitate, you were inclined to believe, until you 

 made the experiment yourself, that Dr. Mansell must 

 have made a wrong calculation as to the quantity of 

 iodide of potassium (680 grains) which lie stated was 

 sufficient to dissolve a 100-grain precipitate, as the 

 difference appeared so small for a solution more than 

 one-third stronger. 



The small difference referred to with respect to the 

 quantity of iodide of potassium required, is owing to 

 the amount of water used being in both cases the same. 

 A slight difference in the strength of a solution of 

 iodide of potassium makes a great difference with 

 respect to the quantity of iodide of silver it is capable 

 of dissolving. Thus, if you remove a small proportion 

 of the water from a solution of the double iodide of 

 silver by evaporation, the slight increase of strength 

 which the solution will thereby acquire, will enable it 

 to take up a much larger proportion of iodide of silver 

 than it already contains ; and if, on the other hand, 

 you dilute it with a small proportion of water, its di- 

 minished strength (unless the solution contains a great 

 excess of iodide of potassium) will cause the precipi- 

 tation of a large proportion of the iodide of silver. 

 And hence the great variation in the amount of iodide 

 of potassium which is found requisite to form a solution 

 of the double iodide of silver, under the same apparent 

 conditions with regard to the proportions of the other 

 ingredients employed, may be accounted for by the 

 impossibility of measuring off with sufficient accuracy 

 the proper proportion of water. 



Whenever exact quantities of liquids are required, 

 recourse should always be had to the balance, for no 

 great accuracy can be depended upon by measurement 

 with our ordinary glass measures, even supposing them 

 to be correctly graduated, which is not always the 

 case . J. Leachman. 



Dr. ManseWs Process. — Dr. Mansell's lucid and 

 very practical paper on the calotype process in " N. & 

 Q.," must, I am sure, be of the greatest service to pho- 

 tographers in general ; and as one of the many I am 

 irresistibly tempted to offer my sincere and hearty 



