THE AMERICAN MONTHLY 



[May, 



the solution after it hjis done its work 

 and proceed with the washing in the 

 developing pan. This avoids soiling 

 the fingers. 



Ferrous oxalate is used repeatedly, 

 so lift the plate out and wash it in the 

 hands. 



As soon as the developer is washed 

 out the plate can be taken out into 

 the light, and all subsequent operations 

 can be conducted in daylight, at any 

 convenient time. If the weather be 

 warm, howe\'er, there is danger of 

 frilling, that is, of ruffling of the film 

 from the glass. To avoid this the 

 plate may be placed in a saturated 

 solution of alum for a few moments, 

 and then throughly washed. After that 

 it may be kept indefinitely, either in 

 water or dry. It is desirable, however, 

 to finish the plates without permitting 

 them to dry. If there are no signs of 

 frilling when the developer is washed 

 off, proceed as follows : When ferrous 

 oxalate has been used for 

 developing, place the plate 

 in the fixing solution, com- 

 posed of one ounce of sodium 

 hyposulphite dissolved in 4 

 ounces of water. This dis- 

 solves the silver salt from 

 the film, and so fixes the 

 picture. I'he fixing is com- 

 pleted when there is no white 

 or opalescent appearance to 

 be seen by looking at the 

 under surface of the plate. 



Wash the plate thoroughly 

 under a tap, or by soaking, 

 until the hyposulphite is en- 

 tirely removed. Then place 

 it for five minutes in a satu- 

 rated solution of alum, wash 

 again, and then stand it up 

 to dry. 



After development with pyrogallic 

 acid, the gelatin film is found to be of 

 a yellow color, which is very objection- 

 able. There are several methods of 

 removing the color, the most common 

 being the use of a solution of alum 

 containing some acid — citric, oxalic, 

 hydrochloric or sulphuric — either 

 beffjre or after fixing. We have 



found the most effectual means to be 

 the use of a solution of 2 drachms of 

 oxalic acid in 10 ounces of water, 

 immediately after washing off the 

 developer. The plate may remain in 

 this solution five or ten minutes, after 

 which it is washed and fixed. We 

 have not found it necessary to use alum 

 after the oxalic acid, but in warm 

 weather it may be required. 



( To bi Continued. ) 



A New Daphniii. (Fig. 17.) 



In the summer of 1879 I found in 

 the waters of Fox River, Appleton, 

 Wisconsin, a Daphnia which seems to 

 have escaped notice hitherto, and 

 which certainly is not figured in any 

 of the descriptions of the Entomostraca 

 of this countrv. 



As will be seen bv the figure, its 



Fig. 17. — Daphnia Kiirusses. 



peculiarity is a remarkable helmet-like 

 enlargement of the head, curved back- 

 ward with a broad thin blade or crest. 

 The figure was drawn by (\amera, and 

 the specimen was not different from 

 its fellows which were abundant in the 

 river and mill-race near the city. On 

 submitting the drawing to Prof. S. I. 

 Smith, he gave the opinion that no 

 similar species had been described in 



