172 



NOTES AND QUERIES. 



[Sept. 1. 1855. 



again brought forward this interesting subject. He 

 stated, that farther experiments had modified M. de 

 Beauregard's theories. He had at first thought that it was 

 the intensity of the negative which caused the different 

 colours in the positive, by the more or less strong action 

 of the light ; he has since ascertained that the light 

 acts upon the negative itself in such a way, that the 

 different coloured rays produce on it, colours analogous to 

 those which appear in the positives. 



M. Durieu exhibited both positives and negatives, in 

 which the natural colours were shown. 



The president, M. Regnault, remarked, that according 

 to this theory the negative ought to show colours com- 

 phmentary to the natural colours of the object, so that the 

 positive, taking the complementary colour of the negative, 

 will produce the actual colour of the object. He con- 

 sidered that, for the purpose of properly investigating the 

 subject, photographs should be taken of the rays of light 

 passing through coloured glass or gelatine, and of the 

 solar spectrum ; natural objects, such as flowers, for 

 example, giving a light too complex in its character. 



M. Durieu stated that M. de Beaure'gard considered the 

 peculiar nature of the collodion he employs exercises an 

 influence upon the coloration. His process is as follows : 



As soon as the cotton has been attacked by the nitric 

 acid, it is plunged into hydrochloric acid in the proportion 

 of 85 grammes of cotton to 125 grammes of acid, and 

 there left, taking care to stir it from time to time, until 

 nitrous acid is evolved. It is then plunged at once into 

 a vessel (not of metal) filled with pure water and washed, 

 and then treated for two hours in a drying apparatus. 

 As soon as the cotton is dry it is dissolved" in 



760 grammes of ether of 62 degrees ) in ' 



240 grammes of alcohol of 40 degrees j summer. 

 840 grammes of ether of 62 degrees ) in 



160 grammes of alcohol of 40 degrees j winter. 



The collodion thus prepared is submitted to a current of 

 chlorine gas until it has acquired a bluish colour. 

 The following are the proportions for iodizing : 



To collodion prepared as above 1000 grammes. 



To iodide of ammonium - - 8 grammes. 



To iodide of zinc - - - 4 grammes. 



To bromide of ammonium - 1 gramme. 



When these substances are completely dissolved, two 

 drops of pure ammonia are added, in order to neutralise 

 any acid which may have been set free. 



The collodion thus prepared should be kept in a cool 

 place, protected from a strong light. It is fit for use at the 

 end of five or six days. However red it appears at first, it 

 will have become of a golden yellow, and clear. It is 

 sensitised in a bath of nitrate of silver of six per cent., to 

 which is added for every 100 grammes of water 10 drops 

 of the following solution : 



Distilled water - - - - 100 grammes. 



Iodide of zinc - - «• - 1 gramme. 



Nitrate of silver - - - - 1 gramme. 



Liquid ammonia - - - - 2 drops. 



Chloride of bromine - - - 1 drop. 



The developing solution is composed of — 



Crystallisable acetic acid - - 18 grammes. 



Crystallised citric acid - - 2 grammes. 



Acetate of zinc - - - - 1 gramme. 



Pyrogallic acid - - - - l gramme. 



Distilled water - - - - 300 grammes. 



As soon as this solution is made, two drops of the fol- 

 lowing mixture are added : 



Terchloride of gold 

 Distilled water 

 No. 305.] 



1 gramme. 

 200 grammes. 



The whole is shaken, and left for two days, and then 

 filtered. 



If the image is too faint, it may be strengthened, even 

 after the fixing, by the following'solution : 



Distilled water - - - - 200 grammes. 



Terchloride of gold, dissolved as above 25 grammes. 



Nitrate of zinc - - - - 20 grammes. 



Nitrate of iron - - _ - 1 gramme. 



This mixture will only keep a very short time in solution. 

 The fixing is done by means of a solution composed as 

 follows : 



Cyanide of silver 

 Cyanide of potassium 

 Cyanide of zinc - 

 Distilled water - 



- - 8 grammes. 



- - 10 grammes, 



- - 1 gramme. 

 - 500 grammes. 



This solution, when filtered, may be employed at once. 



M. de Beauregard preserves the strengthening solution 

 for an indefinite time by reducing it to the solid state, 

 and only dissolving such a quantity as he requires at the 

 time. In the same manner he prepares in the solid state 

 the different baths the composition of which has been 

 given above, and also the collodion itself; so that they 

 can be easily carried about, and preserved without any 

 alteration, up to the moment they are wanted. 



Deepening or Intensifying Collodion Negatives. — The 

 following method I have worked out very successfully 

 during the manipulation of some of my preserved plates, 

 which had suffered in intensity from over-exposure or 

 from using too strong a solution of cyanide of potassium 

 for clearing the plate, viz. while the collodion is still 

 moist (that is, previously to its being dried), wash it with 

 distilled water, and drain for a few seconds ; then cover it 

 rapidly with some fresh pyrogallic acid developing solu- 

 tion, to which a small quantity of nitrate of silver has 

 been added, and carry on the development ; which will 

 proceed just as if the iodide of silver had not been re- 

 moved, with the advantage that there is no chance of 

 staining the transparent part. The strength of solutions 

 used are as follows : 



Water - - - 

 Pyrogallic acid - 

 Acetic acid (common) 

 (or, glacial acid 

 Mix. 



- 5 drachms. 



- 2 grains. 



' 3 drachms. 

 ^ drachm.) 



Of the above I take one volume, and add it to three 

 volumes of water ; and to each ounce of the mixture add 

 ten minims of a 30 -grain solution of nitrate of silver. 



When the intensity of the negative is sufiicient, wash 

 copiously with common filtered water. 



If the plate has once been dried, it is much more difficult 

 to operate upon, and only a small increase of the inten- 

 sity can be obtained by the above method ; but if the 

 course of proceeding indicated be adopted, almost any 

 amount of intensity may be produced. Geo. Shadbglt. 



ISiti^liti to Minax ^\ittiz&. 



Health of Tobacco Manufacturers (Vol. xii., 

 p. 39.). — The facts which Mk. Bates has col- 

 lected relating to the manufacture of tobacco 

 abroad are I think fully borne out by the ex- 

 perience of English manufacturers. 



For some years past I have noticed the freedom 

 of our workpeople from epidemic attacks. There 



