25 



tive, yellow on a white ground. From five to twenty minutes 

 is usually required to produce the effect. In either case, if the 

 picture be washed over with a solution of nitrate of silver, a very 

 beautiful positive picture results. To fix the picture, wash it 

 immediately in pure water, and dry it. If the water contains any 

 muriates, the picture suffers, and long soaking entirely destroys it. 

 When a few grains of common salt are added to the water, a 

 curious effect is produced. The picture is apparently rapidly 

 destroyed, but may be restored by an exposure to the sun of from 

 ten minutes to a quarter of an hour, and is now of a lilac colour, 

 the shades depending on the quantity of salt used. No fresh 

 process is required to fix it. 



A beautiful variety of the Chromotype is thus described by Mr. 

 Hunt. " A neutral solution of the chloride of gold is mixed with an 

 equal quantity of the bichromate of potash. Paper is washed with 

 this solution, and dried near the fire. On exposing this paper to 

 light, it speedily changes, first to a deep brown, and ultimately to 

 a blueish black. If ah engraving is superposed, we have a negative 

 copy, blue or brown, upon a yellow ground. If this photograph is 

 placed in clean water, and allowed to remain in it for some hours, 

 very singular changes take place. The yellow salt is all dissolved 

 ont, and those parts of the paper left beautifully white. All the 

 dark portions of the paper become more decided in their character, 

 and accordingly as the solarization has been prolonged or other- 

 wise, or the light has been more or less intense, we have either 

 crimson, blue, brown, or deep black photographs of a most beautiful 

 character" * 



AMPHITYPE. 



This is another of the interesting and valuable discoveries of 

 Sir John Herschel. It was given to the public at the last meeting 

 of the British Association, and is described by him as follows : 



Paper, proper for producing an amphitype picture, may be 

 prepared, either with the ferro-tartrate or the ferro-citrate of the 

 protoxide or the peroxide of mercury, or of the protoxide of lead ; 

 by using creams of these salts, or by successive applications of 

 the nitrates of the respective oxides, singly or in mixture, to the 



Researches on Light, by Robert Hunt, 1844. 



