HARDWICKE'S SCIENCE- GO S SI P. 



231 



use of, as in the case of asphalt and gold size, that 

 its objectionable quality of spreading and running 

 in is so prominent ; but here again this defect is 

 yery commonly made more active by its being used 

 in too great a proportion, instead of only just suffi- 

 cient to destroy the brittleness of the asphalt ; 

 although even then, if it be used over a layer of the 

 lac varnish, it will scarcely be possible for it to do 

 mischief in any way. 



,TV. Kencely Bridgman. 



MICROSCOPY. 



New Medium for Mounting.— I am desirous 

 of directing the attention of your readers who are 

 working with the microscope, to make trial of a 

 new medium for preserving objects. I 

 have not been able to give it much trial, 

 but I think it promises to work well, and 

 therefore I request some space in your 

 columns. I have for a long time desired 

 to obtain a medium which will receive 

 without disturbance a specimen which 

 has been subjected to the action of gly- 

 cerine, or perhaps carbolic acid, the 

 medium being one which does not remain 

 fluid, but will set. I think I can propose 

 one which is worth trial, or may lead to 

 the formation of a better. I, however, 

 think it needful to any who may be disposed to try 

 it, to institute a few easy experiments before fully 

 following out the trial of the medium I propose. I 

 employ chloral hydrate as a basis. This chemical 

 compound will dissolve and unite perfectly with 

 many substances, and from some of its combina- 

 tions we may obtain mediums which may vary 

 from a fluid to a jelly-like or gum-like consis- 

 tence. Chloral hydrate, besides uniting with gum 

 and resins, also unites with alkaloids; as salicinine, 

 quinine, and cinchonine. Place a small portion of 

 chloral on a glass slide, add a little portion of water, 

 and a nearly equal bulk of either of the above ; gently 

 heat over a flame, mixing the two materials with a 

 needle or glass rod : these will unite, and when 

 cooled be found to be viscid and clear. To such a 

 mixture camphor can be added or glycerine. If a 

 number of such experiments be conducted, the 

 operator will soon find out what he is likely to obtain, 

 and thus contrive a new medium suited to some 

 objects. I propose the following : — Make a nearly 

 saturated solution of chloral in water; filter, and then 

 add sulphate of cinchonine to near saturation. A 

 portion of this combination is placed on a slide, 

 heated slightly and allowed to cool. The object is 

 then placed in it and the cover applied, which, 

 however, requires to be cemented with gum solu- 

 tion, and then Bell's cement or Canada balsam. To 

 this " artificial balsam," as I am inclined to call it, 



I have added a little dextrine, so as to render it 

 more solid. .Your workers can make trial, and 

 report on it. Glycerine and dextrine together 

 boiled, and then chloral hydrate added, make a clear 

 solution, which, I think, may be tried also. — 

 Thomas Shearman Ralph, Assoc. Linn. Soc. Load., 

 Kew, Melbourne. 



Polabiscope Apparatus. — Presuming others 

 would be glad of simple additions to the micro- 

 scope, I have ventured to send you a full-sized sketch 

 of apparatus I have made for use with the polari- 

 scope. A, a disk of talc (probably selenite would 

 do better) fitted in the end of a pin, so that it may 

 be revolved and placed at any angle with the object. 

 The effect produced is very beautiful, the ground 

 colour changing with the slightest variation of the 



Fig. 142. Polariscope Apparatus. 



Fig. 143. Disk of Talc fitted in Pin. 



S^_ 



.J 



Fig. 144. Fitting for revolving Stage. 



position of the disk, giving blue, green, purple, 

 orange, violet, &c. It will be found necessary to 

 revolve the prisms or stage, as sometimes, after 

 altering the angle of the disk, no colour appears ; 

 but the slightest movement of the revolving stage 

 of the microscope gives the ground colour. B is 

 the fitting for it : the bottom part fits into the object- 

 holder on the stage. C is a small spring to keep 

 the object in position.— George leggett, Norwich. 



The Bramhall Oblique Illuminator.— In my 

 last communication about my Oblique Illuminator, 



