70 



THE AMEKICAN MONTHLY 



[April, 



H. L. Smith, wrote to me that he had 

 found some new resins, of which one 

 possessed an index of refraction of i .63. 

 I replied to him the same day that 

 two products of this kind, styrax and 

 liquidamber, had been known to me 

 for some time, having fovmd them 

 during my researches upon homoge- 

 neous Hquids, and I proposed to pub- 

 lish our results together. 



" As I proposed to employ styrax 

 exclusively for the series of which I 

 begin the publication next month, the 

 time has come to make known the 

 properties of this product. Never- 

 theless, I would prefer to delay the 

 publication, in order to join the name 

 of Mr. H. L. Smith with mine. 



" Up to this time I have received 

 no response, and I therefore do not 

 know if the products he has employed 

 are the same as mine." 



The author then refers to the use 

 of naphthaline monobromide with a 

 refractive index of 1.65 in the study 

 of diatoms, adding that this substance 

 can never come into general use 

 owing to the difficulty of closing the 

 cells containing it, and to its disagree- 

 able odor. 



In seeking for a natural resin which 

 could be employed instead of the 

 naphthaline bromide, with an index 

 of refraction high enough for a homo- 

 geneous immersion liquid, two were 

 discovered, styrax, from the Liquid- 

 ambar orientalis^ Mill, from Asia 

 Minor, and the liquidamber furnished 

 nished by the Liquidambar styraci- 

 Jltca^ L., of North America. 



Both these products have been 

 used by Dr. Van Heurck for a con- 

 siderable time, but the results were 

 not published until the preparations 

 had been kept long enough to test 

 their durability. 



The author believes that the mounts 

 are much less alterable than those 

 made with Canada balsam, which 

 becomes resinous after some time. 



Purified styrax contains a granular 

 substance which must be removed by 

 dissolving in chloroform and filtering 

 the solution. The solution thus ob- 



tained is used in the same manner as 

 the solution of Canada balsam. Styrax 

 and liquidamber are quite as easily 

 employed as balsam, and they do not 

 form bubbles of air on heating. 



Diatoms are beautifully shown when 

 mounted in either styrax or liquid- 

 amber, and their details are resolved 

 with great ease. Amphipleura pel- 

 lucida, for example, shows its striae in 

 a very perfect manner. The author 

 believes that styrax will supplant Can- 

 ada balsam for movmting, owing to 

 its great advantages. 



It is well to expose the styrax as 

 purchased, in a thin layer to the sun 

 for several weeks. In this w^ay much 

 of its yellow color is discharged, the 

 water it contains evaporates, and it 

 becomes hard. It may then be dis- 

 solved in chloroform, as already de- 

 scribed. Instead of chloroform, ben- 

 zine, or a mixture of benzine and 

 absolute alcohol, may be employed 

 in making the solution. 



Having given Dr. Van Heurck's 

 observations, it remains to add our 

 own experience with the styrax ob- 

 tained from a druggist in Washington. 

 The styrax, or storax, was a pasty 

 mass of a light dirty gray color, a 

 very unpromising material for a 

 mounting medium. A portion was 

 placed in a test-tube, shaken with 

 chloroform and thrown upon a filter. 

 The filtrate was clear , but rather deeply 

 colored. This was used for mounting 

 a few specimens of diatoms. It only 

 required a few moments to prepare 

 the small quantity of solution used 

 in the experiments. 



As regards the results, we can say 

 that it works very much like balsam. 

 Its value as a mounting medium for 

 certain objects, such as a diatoms for 

 example, has not been overstated by 

 Dr. Van Heurck. We shall use it 

 ourselves hereafter instead of balsam 

 for diatoms. The comparative ex- 

 periments made by us have clearly 

 demonstrated its superiority for this 

 purpose. A fine slide of diatoms 

 movmted in balsam by Prof. Kellicott, 

 a pure gathering of Stephanodiscus 



