1886.] 



MICKOSCOPICAL JOUENAL. 



177 



a formula for what he regards as the best 

 cement. Mr. E. A. Schultze has translated 

 the article for the Joiirn. iV. Y. Alicr. Soc. 

 After discussing the merits of various resins 

 used in varnishes, he gives the following 

 instructions for preparing his cement : — 



' Taking equal parts of the best, clearest, 

 and hardest amber-varnish and copal-var- 

 nish, mix them and heat until all the tur- 

 pentine has disappeared. This will require 

 a temperature of ioo°to i5o°R. As soon 

 as all the turpentine has evaporated, re- 

 move the dish from the flame, allow it to 

 cool somewhat, and then add oil of laven- 

 der to the liquid in proportion of j4 to i ; 

 mix well, and allow the entire mass to cool 

 thoroughly. The process is terminated by 

 adding from 20 per cent, to 40 per cent, of 

 artificial cinnabar (eosin with cinnabar), 

 which should be very carefully and thor- 

 oughly rubbed in. The best method for 

 rubbing in the cinnabar is that employed 

 in the preparation of fine oil-paints. Should 

 the cement when finished be too thick for 

 use, as inuch oil of lavender as will give 

 the required fluidity may be added. The 

 component parts and their proportions 

 would then be as follows : — 



Amber 25 parts. 



Copal 25 " 



Linseed-oil varnish ... 50 " 



Oil of lavender 50-60 " 



Artificial cinnabar . . . . 40-60 " 



We are quite at a loss to understand the 

 parenthetical expression ' eosin with cin- 

 nabar ' as applied above, but in the form- 

 ula itself the expression is ' eosin or cin- 

 nabar,' which is probably what the author 

 intended to write, the eosin being added 

 to impart color, although in this case the 

 proportion given would be excessive. The 

 addition of oil of lavender is to be highly 

 commended. For a cement that depends 

 upon the drying of the resins and oil, rather 

 than the evaporation of a volatile solvent, 

 we have no doubt this one of Dr. Heyden- 

 reich is the best. 



— This matter of ceinents recalls to mind 

 an expression in the Zeitschrift, above 

 mentioned, applied by Dr. Griesbach to 

 ourselves. In describing the method 

 given by us sometime since for prepar- 

 ing shellac cement, he referred to us as 

 ' ein eifriger Anhiinger des Schellackce- 

 mentes.' We are quite satisfied with the 

 appellation, for with nearly ten years ex- 

 perience with shellac, using it for the great 

 variety of preparations that naturally come 

 to a general observer in microscopy, we 

 may say it is the only cement that has 

 come into our hands (and we have tried 

 many) that never fails. But apart from 



this, there is another reason why we have 

 so persistently urged its use in these col- 

 umns, until we doubt not many of our 

 readers are tired of it, and are inclined to 

 regard us as a crank on the subject. The 

 reason is that so many of the best observ- 

 ers and students do not mount specimens 

 for preservation because they have not the 

 time to spare. There is just reason for 

 this if the ordinary methods of mounting 

 in fluids are followed, while Canada bal- 

 sam is not the proper medium. But by 

 using shellac, a permanent mount dry in 

 water or in glycerin can be made on a 

 perfectly plain slide in five minutes, and 

 it will keep perfect for years. 



— We are also reminded that in several 

 of the photographic journals the method 

 of clearing shellac solution with ' petro- 

 leum spirit' or ' gasoline ' recommended 

 by us * has been condemned, and the 

 assertion made that for various excellent 

 reasons the plan will not answer the pur- 

 pose. In this case, however, the results of 

 experience are not in strict accord with the 

 theories of the critics. The plain fact is 

 that the plan does work ; otherwise we 

 would not have published it. But to show 

 to what extent the principle of it has been 

 misunderstood, and also the coolness with 

 which improvements upon well-tried meth- 

 ods are sometimes suggested by persons 

 who do not understand the subject, we 

 may refer to a leading article in one of 

 our contemporaries. After explaining why 

 our plan will not work, the writer suggests 

 that it might be better to first treat the dry 

 shellac with the petroleum derivative, for 

 the purpose of dissolving out that portion 

 not soluble in alcohol, after which a clear 

 solution in alcohol might be obtained. We 

 need only say that the naphtha in our 

 experiments did not dissolve the matter 

 insoluble in alcohol, but effected a mechan- 

 ical separation of it. 



CORRESPONDENCE. 



To THE Editor : — I notice, in June 

 number of Microscopical Journal, a 

 complaint concerning oxide of zinc ce- 

 ment. I think Mr. Claypole's annoyance 

 has been caused by impurity of the zinc 

 oxide used. Very little of the oxide, as 

 purchased, is pure, as it contains a portion 

 of the carbonate, due to exposure to air, 

 from which it takes up carbon dioxide. 

 If the oxide is exposed to a gentle heat 



* Vol. v., p. 121. 



