82 



THE AMERICAN MONTHLY 



[May, 



Preparation of the Ethyl Ether of 

 (jallic Acid. 



R. DORSEY COALE, PH. D. 



At the request of Prof. Christopher 

 Johnston, I send a description of the 

 method of preparation of the ethyl 

 ether of gallic acid. Of course this 

 method of preparation is not original 

 with me, and my only object in send- 

 ing this description is to enable the 

 readers of the Journal to prepare for 

 themselves, or to have prepared for 

 them, this substance which, in the 

 skilful hands of Prof. Johnston, has 

 proved to be such a beautiful object 

 for the polariscope ; for, although it 

 can scarcely be considered a rare sub- 

 stance, it is not one which would be 

 likely to be found in the stock of most 

 dealers in chemicals. 



The ethyl ether of gallic acid, or 

 ethyl gallate, can readily be prepared 

 by passing dry gaseous hydrochloric 

 acid (generated by the action of sul- 

 phuric acid upon ordinary salt) 

 through an alcoholic solution of gal- 

 lic acid. 



When the solution is saturated with 

 hydrochloric acid it is evaporated to 

 dryness on a water bath, the residue 

 redissolved in hot water, the excess 

 of acid neutralized by the addition of 

 finely powered chalk, and the mix- 

 ture filtered. The clear filtrate left to 

 itself yields, on cooling, long needles 

 which are usually colored dark brown, 

 but can readily be purified by one or 

 two recrystallizations from water. 



When pure, ethyl gallate crystal- 

 lizes in small oblique prismatic 

 needles which are yellow, brilliant, 

 and transparent when wet, and opaque 

 white or slightly yellow when dry ; 

 it is but little soluble in cold water, 

 but is readily soluble in hot water, 

 alcohol, and ether. 



The process of preparation is very 

 simple, but, like most of such pro- 

 cesses, requires some care and neat- 

 ness to obtain the best results ; and 

 upon the purity of the substance its 

 beauty as a microscopic preparation 

 seems in great measure to depend. 



University of Maryland. 



An Eye-shade for Monocular 

 Microscopes. 



BY R. H. WARD, M. D., F. R. M. S. 



In using a monocular microscope 

 much of the fatigue, both to eye and 

 brain, is avoided by habitually em- 

 ploying a shade in front of the unused 

 eye. A maximum of comfort seems 

 to be attained, not by a large shield 

 that completely darkens one eye, 

 which itself becomes tiresome by 

 reason of the great contrast with the 

 intensely illuminated eye over the 

 microscope, but by a stop of moder- 

 ate size and at some distance from 

 the eye, which, while preventing the 

 confusing efiect of an image in the un- 

 used eye and the fatiguing effort re- 

 quired to keep the observer's attention 

 confined exclusively to the microscop- 

 ical image in the other, still allows the 

 entrance of much diffuse light, and 

 permits, without abrupt transfer from 

 darkness to light, the frequent changes 

 required from rest over the shade to 

 inspection of books or memoranda or 

 of other objects upon the table. 



Having recently had occasion to 

 employ a monocular instrument for 

 certain purposes, after having used 

 the binocular exclusively for more 

 than fifteen years, the writer has been 

 led to recall an almost forgotten form 

 of shade which he contrived and used 

 with great comfort some twenty-five 

 years ago. Doubtless individuals 

 have often made just as good and 

 simple shades for their own use ; but 

 the writer has never happened to no- 

 tice one, either made or described, 

 and he therefore brings this forward 

 in the hope that it may thereby be- 

 come as useful to some others as it 

 has been to himself. His experience 

 leads him to believe that some such 

 contrivance should always remain 

 fixed upon a monocular microscope 

 while it stands upon the table ready 

 for use, even occasional glances into 

 the tube being more tiresome without 

 this accessory than with it. 



It consists, as shown in fig. i8, of a 

 circular disk of hard rubber or black- 



