MICHIGAN ACADEMY OF SCIENCE. 93 



SODltM SILICATE AS A MOUNTIXG MEDIUM. 



,J. B. DAXDEXO. 



For the past five years, off and on. we liave used sodinni silicate as a 

 convenient medium for mounting fresli specimens of various Iviuds, and, 

 for certain purposes, it luis i)roved very useful. Sodium silicate, some- 

 times called soluble glass, has been used as a cement for crockery and 

 glassware, and more recently also as a jireservative of eggs, — the sodium 

 silicate being spread over the surface of the shell as a glazing. 



As a medium for mounting hi.>tological preparations, sodium silicate 

 was suggested to us by I*rof. Kedzie a few years ago and brought to 

 our laboratory by a former student, ]Mr, Loew. In our laboratory, we 

 often run across accidentally, sometimes through students, sometimes 

 in our own work, specimens Avhich show certain things particularly well, 

 and it is often desirable that such should be kept permanently. This 

 occurs more frequently in investigating fungi or fungous diseases of 

 plants. Glycerine and balsam are practically the only permanent mount- 

 ing media now in use, and glycerine is a very poor affair, because it 

 never solidifies; and in handling, the cover glass is likely to be moved 

 and very frequently the specimen destroyed. Glycerine mounts can hr 

 kept permanently but they have to be ringed with a suitable material, 

 and even then, a cousideraljle proportion is sure to be destroyed. With 

 regard to balsam, tlie work of dehydration and preparation is so long, 

 that a specimen would be almost certainly lost in the process. 



It is here where sodium silicate comes in, as it mixes perfectly with 

 water and hardens in a day or two, so that, if one happens upon a few 

 spores of this, a few asci of that, or of any other particularly desirable 

 structure, he can, by the addition of a drop of sodium silicate, preserve 

 the specimen indefinitely. This substance does not mix well with glycer- 

 ine or alcohol and must be used with water. It can be put on the 

 specimen either by removing the cover glass and placing the drop in the 

 ordinary way, or by drawing a drop under the cover. The former is 

 the more satisfactory unless there is danger of losing the specimen in 

 lifting the cover. 



Sodium silicate has some advantages and some disadvantages which 

 shall be pointed out : 



Advantages: — (1) It is convenient, always ready, and makes perma- 

 nent specimens directly from water. (2) Its optical qualities render 

 it one of the very best known, as its index of refraction is nearly the 

 same as glass. (3) It is slightly alkaline in reaction and does not shrink 

 or plasniolyze fresh material, in some cases preserving even the color 



Disadvantages: — (1) If the objective of the microscope becomes 

 smeared (accidentally of course) with it, and if left so for a few days, 

 the objective is s}>oiled, as the silicate unites with the glass of the ob- 

 jective. If, however, it be cleaned right away, and especially with a drop 

 of diluted hydrochloric acid, no harm is done. (2) It tends to become 

 whitish around the edge of the cover in a few years and looks bad and 



