SCIENTIFIC SUMMARY. 
441 
It is to be hoped that the rewards offered this year for the first time may 
serve as a stimulus to increased exertion on the part of the contributors 
to future exhibitions of the Photographic Society. 
His Majesty the Emperor of the French has bestowed the cross of the 
Legion of Honour upon three photographers whose productions were most 
deserving of attention in the late International Exhibition ; viz., M. 
Bayard, for useful photographic inventions ; M. Duboscq, for improve- 
ments in optical instruments ; and on M. Poitevin, for his inventions in 
carbon printing and photo-lithography. 
The premium of 2,000 francs offered, in the year 185G, by the Due de 
Luynes, for the best method of printing in carbon, has ultimately been 
divided into four minor prizes, and bestowed as follows : — A gold medal of 
the value of 600 francs was given to M. Poitevin, as the originator of the 
first idea upon which the carbon printing processes were based ; viz., the 
peculiar action of light upon a combination of organic matter with salts 
of chromium. The merit of this invention appears, however, to rest 
with Mr. Mongo Ponton, who as far back as May, 1839, communicated to 
the Royal Scottish Academy of Arts his discovery of the action of sunlight 
upon paper steeped in a solution of the bichromate of potash. The second 
gold medal, of equal value, was bestowed upon MM. Davanne and Girard 
for their researches into the causes of the fading of silver prints. A 
silver medal valued at 400 francs was awarded to Messrs. Gamier and 
Salmon, for their process of printing in carbon ; and a similar medal was 
given to Mr. Pouncey, of Dorchester, for his invention of the same 
character. Subsequently the reward conferred upon M. Poitevin has 
been augmented by 2,000 francs, and an additional medal presented to 
M. Fargier for his process. 
The practical photographer is indebted to M. Meynier for two valuable 
suggestions. The first refers to the use of the double sulphate of iron and 
ammonia as a developing agent. The aqueous solution of this salt pos- 
sesses the advantage of greater permanence, whilst as a reducing agent it 
is eqally efficient with the simple sulphate. Several distinguished operators 
have pronounced very favourably upon the capabilities of this salt as 
readily giving exquisite half-tone with a proper amount of intensity in 
the high lights. It is manifestly requisite to employ such a larger pro- 
portion of this salt as will compensate for the diminished amount of 
actual protoxide of iron in the compound ; a solution containing 25 
grains of the double sulphate, with 25 minims of acetic acid to the 
ounce of water, is stated by Mr. G. Wharton Simpson to give excel- 
lent results. The second suggestion, offered by M. Meynier, has reference 
to the employment of the sulpho-cyanide of ammonium as a fixing 
agent, both for negatives on glass and prints upon paper. This com- 
pound has the property of dissolving both the iodide and chloride of 
silver, forming solutions which are not liable to the deposition of the 
black sulphide on heating or standing at rest for some time. The pro- 
position has been made the subject of experiment, and reported upon 
by Mr. Spiller, who states that this re-agent is the only one known 
to have the power of removing the whole of the silver from the pre- 
served white portions of albumenized prints, and that the cost of this 
