66 



THE AMERICAN MONTHLY 



[April, 



until it will flow freely from a brusli, 

 for use in finishing^ slides. 



3. Asphalt or I3runswick-black. 

 Either of these can be purchased 

 from dealers better than they can 

 be made, without considerable 

 trouble to procure the proper 

 materials. 



4. Gold-size. This can be pur- 

 chased from dealers in artists' 

 materials. It is a good cement, 

 but the writer never uses it alone. 



5. Asphalt and Gold-size. Mix 

 one part of good asphalt-cement 

 with one part of gold-size. For 

 fluid-mounts in general, there is no 

 better cement known ; but it must 

 be used strictly according to the 

 directions, which will be given in a 

 future article. 



6. Shellac. A solution of shellac 

 in alcohol is indispensable. The 

 common shellac is good enough, for 

 the color does not show on the 

 finished slide. The simplest way 

 to make a small quantity, is to dis- 

 solve the shellac in alcohol and 

 wait for the insoluble portion to 

 settle, so that the clear solution can 

 be poured ofi^. A little mastic can 

 be dissolved in the alcohol, by heat- 

 ing, and will give greater elasticity 

 to the cement. 



1. Glycerin-jelly is a convenient 

 mounting medium. It is advisable 

 to purchase this, or else use in its 

 stead, Deane's "gelatin medium." 



All these cements should be kept 

 in wide-mouthed bottles provided 

 with good corks, through which a 

 suitable brush is passed. By keep- 

 ing the neck of the bottle clean, 

 this method answers very well. A 

 wire or a glass rod passed through 

 the cork of the balsam and glycerin- 

 jelly bottles, is very convenient for 

 taking out portions as required. 



In addition to the cements en- 

 umerated, a few others may be used 

 for special purposes with advantage, 

 but they are not necessary. They 



will be referred to in the proper 

 places. 



For dry-mounting, some brass 

 curtain-rings, selected to fit the 

 covers, are very useful ; but the wax- 

 cells described by Dr. Hamlin * 

 are quite as good, and more readily 

 adapted in size, depth, etc., to the 

 various objects. 



There are but few instruments 

 necessary for mounting purposes, 

 and these need not be enumerated. 

 We will only say that a pair of cheap, 

 brass forceps, a few needles mounted 

 in wooden handles, a spirit-lamp, 

 turn-table, slides and covers, are all 

 that are absolutely necessary. The 

 covers should be of three sizes, the 

 most useful measure respectively, 

 ^, ^, and 7^ of an inch in diameter. 



Procuring and Cleaning 

 Biatomaceae. 



It was my good fortune to dis- 

 cover a locality at Citronelle, Ala- 

 bama, very rich in fresh-water forms, 

 and my plan to utilize my "find" 

 was as follows : — I placed about a 

 gallon of the swamp-muck in a 

 bucketful of water, and thoroughly 

 stirred the mass until it became 

 entirely desintegrated ; by this 

 means all of the sand settled at once 

 to the bottom, the water, with the 

 decayed vegetable matter held in 

 suspension, was passed through a 

 coarse sieve to separate the grosser 

 parts, and the water passed again 

 through a sieve with finer meshes ; 

 the resulting vegetable matter was 

 then compressed to drive out as 

 much water as possible. After this 

 treatment, it was spread out on an 

 iron ash-pan from a coal-grate, and 

 then submitted to gradual heating 

 over the grate ; in about half an 

 hour the entire mass was reduced to 

 a very fine ash, on account of the 

 vegetable matter drying, igniting 



This Journal, page 46. 



