BULLETIN 39, UNITED STATES NATIONAL MUSEUM. 



[12] 



exude gTacIually from under tlie edge of the cover, rendering the slide 

 sticky and disagreeable to handle. If too hard, on the other hand, it 

 soon crackles, or perhaps allows the cover to spring off on the occasion 

 of any slight jar. 



Never mount sections for actual work on the long (3-inch) slides such 

 as are (Ordinarily used for histological work, as they project beyond the 

 edge of the stage and interfere with its revolution. 

 The sizes mostly used by petrologists are either 28 

 by 48 mm., or 32 mm. square. The former has been 

 adopted in this department. For ordinary work a 

 21 mm. square cover glass is sufiicient (see fig. 15.) 

 Inasmuch as special care must be exercised in 

 the preservation of the sections, the following is 

 given, although not absolutely germane to the sub- 

 ject in hand. The article is reproduced essentially 

 as it first appeared in Science for I^ovember 25, 1892. 



Bascdk 



BS663. Lou- 



Jia^i^. Olmne-. 

 PLaqtadase' feldspars 



Fig. 15.— Thin section, 



As it happened, we had in stock a number of paste board 

 boxes some 93 millimeters wide, 143 millimeters long, and 48 

 millimeters deep, all inside measurements. The dimensions 

 of our standard slide are 48 by 28 millimeters. By means of 

 two wooden partitions, some 3 millimeters thick, running 

 lengthwise, each box was divided into three equal compartments, the partitions 

 being held in place by glue reenforced by two small tacks at each end. Heavy 

 nianila wrapping paper, such as we also had in stock, was then cut into strips 25 

 millimeters wide and as long as the sheet of paper would allow, in this case about 

 7 feet. These strijjs were then bent into a series of folds, as shown in the accom- 

 panying illustration, the apices being rounded, not pinched flat. If carefully done, 

 the folds when crowded gently together act as a spring. Two of these folded strips 

 were then placed lengthwise in each compart- 

 ment, and the slides introduced, standing on 

 end, between the folds at the top. A box as 

 thus jsrepared readily holds three rows of 50 

 slides in a row, or 150 altogether. 



Each slide is separated from its neighbor in 

 the same row by a double thickness of maiiila 

 paper, which, owing to its manner of folding, 

 acts as a spring, and avoids all possible danger 

 of breakage. When all the compartments are 

 filled, the space between the tops of the slides 

 in any row is but about 2 millimeters; but 

 there is, nevertheless, no difficulty in removing 

 a slide or in getting at it to read the label 

 without removal, since, owing to the yielding 

 nature of the paj)er, the tops may be readily 

 drawn apart. In this respect the box offers a 

 great advantage over those with rigid wooden 



compartments, such as are commonly in use. The first box was made merely as an 

 experiment. It proved so satisfactory that, for the time being at least, it is the form 

 adopted for storing the several thousand slides forming the museum collections. 



I have attempted to show the arrangement as above described in the accompany- 

 ing drawing. In .reality the slides are held much more firmly than indicated, since 

 the paper bulges and comes against both the front and back of the slides, the full 



Flu. IG.— Storage frame 



