198 



THE AMERICAN MONTHLY 



[October, 



— The microscopist who occasionally 

 photographs his specimens finds that his 

 developing solutions deteriorate by keep- 

 ing, and often when he comes to use 

 them, after standing untouched for some 

 time, they do not act properly. Especially 

 is this true of developers containing 

 pyrogallic acid, which, as ordinarily made, 

 soon loose their strength. It is customary 

 to make up the solutions and keep them 

 ready for use, but owing to the circum- 

 stance above mentioned this plan is not 

 a good one for microscopists who only use 

 them occasionally. We have adopted the 

 following plan for developing, which ena- 

 bles fresh solutions to be readily made 

 without loss of time. We have always 

 at hand citric acid and pyrogallic acid in 

 powder, strong ammonia (.880), and a so- 

 lution of potassium bromide, 50 grains to 

 the ounce of water. When about to de- 

 velop the plates dissolve 1.5 grains of 

 citric acid in 8 ounces of water. In prac- 

 tice it is not necessary to weigh out the 

 exact quantity, as it can be measured on 

 the point of a knife, after a little experi- 

 ence. Then take -i drachm of ammonia 

 and mix it with 8 ounces of water. Go 

 into the dark room with the solutions, put 

 the exposed plate into the developing 

 dish, and proceed as follows : For a 

 4X5 plate take one ounce of the citric 

 acid solution and add to it 2 grains of the 

 pyrogallic acid in powder, measuring that 

 quantity in the hand, or on a spatula. It 

 dissolves almost instantly. Then add 

 one ounce of the ammonia solution and a 

 drop or two of the bromide, and flow the 

 whole over the plate. The development 

 proceeds slowly, and may be controlled 

 in the usual manner by adding more 

 bromide, or a few drops of dilute ammonia, 

 as the case may require. 



CORRESPONDENCE. 



A Good Objective. 



To THE Editor. — In your Journal for 

 March you gave us " An evening with Am- 

 phipleura." On the 28th of April, I re- 

 ceived an objective from Messrs. H. R. 

 Spencer & Co. marked "-/^-, Hon. B. A., 

 125''','' \vith the remark, " We think the ^V 

 does the finest work on Podiira that we 

 ever saw." During the month I have 

 tried it pretty thoroughly on the slide of 

 Atnphipleura which I send to you, with 

 the followinsf results. It resolves the sin- 



gle frustules with daylight above or be- 

 neath the stage, with concave mirroralone, 

 in homogeneous fluid or in glycerin. By 

 lamplight and concave mirror with bull's- 

 eye condenser with either fluid. It also 

 resolves them readily by central sunlight. 



I do not regard the ainphipleiira on 

 Moller's probe-platte as a test for our best 

 glasses, and send you some from this vi- 

 cinity, i would be pleased to have you 

 or your triends try the best glasses of 

 other makers, on this slide, and let the 

 public know the results. I have reason 

 to believe that my objective is superior to 

 the one you refer to in your article. 



John Sloan. 



New Albany, Ind., May 30th, 1883. 



[We have been unable to examine the 

 amphipleiira sent by the writer as yet, 

 but will do so at an early day, when our 

 readers will be informed of the results. 

 Absence from home has greatly interfered 

 with practical work with the microscope. 

 — Ed.] 



Cleaning Diatoms. 



To the Editor. — I have for a year or 

 two at times cleaned up a good many dia- 

 toms, and find that a method not de- 

 scribed in any of the books, so far as I 

 know, works better than any of the ap- 

 proved ones. 



The diatoms are to be freed as far as 

 possible from water, by decanting it off. 

 Then covered with a liberal quantity of 

 pure concentrated sulphuric acid, which 

 is heated to boiling in a good porcelain 

 evaporating dish. Continue the heating 

 till the white fumes of sulphuric acid be- 

 gin to escape freely, and then, while still 

 over the lamp, add potassium nitrate 

 (saltpetre) in bits of the size of a pea, 

 waiting after each addition till the effer- 

 vescence ceases before adding more. 

 Continue till the whole mass in the dish 

 is white or light yellow. This will not 

 usually take more than 5 minutes. Then 

 wash the cleaned diatoms with successive 

 portions of distilled water as usual. 



J. Y. Bergen, Jr. 

 Lombard University, ) 



Galesburg, III. ) 



MICROSCOPICAL SOCIETIES. 



The Annual General Meeting for the 

 election of officers was held by the (2uekett 

 Club on the 27th of July, when the follow- 

 ing officers were unanimously elected : 



