Jan. 22, 1885] 



NA TURE 



263 



Roscoe and W. J. Russell, on " Experiments suitable for Illus- 

 trating Elementary Instruction in Chemistiy." These notes 

 appear to me to be very a t*ful as a rough guide to the school- 

 teacher. But unless the teacher is able to arrange the experi- 

 111 :i ;il illustrations so that some conclusions regarding the 

 elementary principles of chemistry hall be drawn from the 

 results he obtains, which conclusions shall then be sub nitted to 

 experimental examination, I think the notes will fail of their 

 object. 



It is to the want of progressiveness in the ordinary chemical 

 it I wish to draw attention. 



The student of physics advances ; he feels his way from one 

 set of phenomena to another ; he generalises, and gets hold of 

 some principles on which he may rest. In the ordinary chemi- 

 cal course the student begins with enthusiasm; he is delighted 

 with the experiments, and he lakes a lively interest in the 

 manipulative failures of the lecturer. But, after a little, the 

 student finds that he is not progressing. When he has been 

 told, and shown, the properties of hydrogen, oxygen, and water, 

 he is expected to ti earing a list 



of properties of niti tides of nitrogen. Then lie fills 



his note-book with many facts regarding ammonia and nitric 

 acid, an. I 



Now I do firmly believe that chemistry is a branch ol 

 and that it may be taught as such. I think it is possible, in a 

 course of lectures on chemistry, to lead the fairly intelligent ami 

 not very idle student fn icts about everyday occur- 



rences to the difficult and apparently remote discussions regard- 

 ing the architecture of molecule-, in which Chemists so much 

 delight. 



It lectures on chemistry were arranged so that principles 

 should be discussed and amply illustrated by well-chosen ex- 

 periments, instead of being (a> I am afraid is still too often the 

 litions of disconnected facts about a string of elements 

 and compounds, I believe this branch of science would rapidly 

 develop in this country. It seems to me that the distinction 

 implied in the commonly-used terms chemistry and. chemical 

 iy is radically unsound. There are not two chemistrys, 

 chemistry. We do not speak of physics as different 

 from natural philosophy. 



What we want is to convince our students that they 

 are dealing with realities. I am continually presented with 

 ■ question-, which perhaps demand a knowledge of 

 the laws of chemical combination, wherein a feu elementary 

 facts are elevated to the rank of an all-embracing theory, 

 and complex structural formula: are dealt with in a style 

 of appalling familiarity, as if they were the topics which it is 

 j to discuss on the very threshold of chemistry. One 

 is told that chlorine is a monad, that i-, it h a "one-armed 

 one " ; and then the conclusion is triumphantly announced, 

 set why it is " that hydrogen and chlorine combine to 

 form hydrochloric acid, and so on. The other day I implored 

 a candidate in a certain examine me a reason for 



writing the f rmula of alcohol C 2 H 6 — I III rather than C.,H 6 ; 

 he told me he had seen the former in a book. This is 

 11 the average student ; an I yet these people call them- 

 selves students of science. I am afraid the teachers are greatly 

 to blame. 



The examiners have undoubtedly much power; but I think 

 thi' examinations in chemistry are improving as a whole. 



\\ In n a lecturer in chemistry announces two series of lectures, 

 one elementary and one advanced, is it not very often found 

 ■I class is condemned to hear copious details 

 regarding the purification and methods of separation of the rare 

 metals, while the elementary class is entertained with an exhibi- 

 tion of the properties and reactions of the simple and compound 

 gases? But is this chemistry? 



I think that the teachers of chemistry must c 

 the time-honoured practice of placidly proceeding from element 

 to element, and from compound to compound ; they must ask 

 themselves whether they 1 now of any reasons why chemistry 

 h of natural science, and, having con- 

 scientiously answered this question, they must try to make their 

 5tU lents really acquainted with these reasons. 



Or. Sydney Young (Nature, vol. xxxi., p. 126) has referred 

 to the paucity of good elementary text-books of chemistry. I, 

 too, have felt the want of a really good book in attempting to 

 teach the principles of chemistry to beginners. Is there any 

 elementary book which treats chemistry as a genuine living 

 science? M. M. Pattison 1 Muir 



Cambridge, January 1 2 



A Method of Isolating Blue Rays for Optical Work 



In many optical experiments, e.g. in examining the d 1 "" 

 of optic axes in crystals, a homogeneous or monochromatic light 

 is required. A fairly homogeneous red light, nearly correspond- 

 Fraunhofer line B, can be obtained by a properly- 

 selected piece of red glass placed in front of a go. . 

 burner or paraffin lamp. For yellow light, nothing can be 

 1 . ii nne of a Runsen's burner in which a bead of 



sodium carbonate is held in a loop of platinum wire. For blue 

 rays, the light transmitted by a solution of cuprammonium sul- 

 phate is generally recommended, since the ordinary blue gla-s 

 coloured with cobalt invariably transmits red rays as well as 

 blue. But the use of a glass cell containing a strong ammo- 

 niacal solution is often inconvenient and unpleasant. 



I have met with a peculiar kind of greenish-blue glass, used 

 for railway signal lamps, and known as "signal-green glass' 

 (coloured, I believe, with copper in its divalent condition), which 

 is remarkably opaque to the less refrangible rays nearly as far as 

 Fraunhofer's line E, while it trai ' quantity of blue 



and some green light. By combining a piece of this glass with a 

 piece of rather deep-tinted cobalt glass, the red rays transmitted 

 by the latter may be whi lly stopped, and only the part of the 



spectrum between F and G is transmitted, constituting a light 

 at any rate not less homogeneous than that transmitted by 

 solution of cuprammonium sulphate. 



This "signal-green glass " is also useful in illustrating selective 

 absorption of light by different media. If, for instance, a piece of 

 it is superposed on a piece of properly-selected red glass, each ab- 

 sorbs what the other transmits, and practically no luminous rays 

 survive the two ; only a faint neutral-tinted light struggling 

 through, even when strong sunlight is used. 



This can be well shown on the screen by fixing a narrow strip 

 of the "signal-green glass" vertically in a lantern-slide, and 

 crossing it with a similar strip of red glass fixed horizontally in 

 the same frame. The square space where the two overlap 

 appears absolutely black. 



The same arrangement is useful for other absorption-experi- 

 ments, since the original colours of the media are shown, as 

 well as the result of their superposition. 



It is necessary to remember that much lighter tints are wanted 

 for lantern-work than for subjective experiments. 



Eton College, January 10 H. G. Madan 



Barrenness of the Pampas 



In the admirable address of Prof. Asa (hay at Montreal, he 

 alludes to the singular absence of trees and herbaceous plants 

 throughout the Pampas or vast level plains of the South Ameri- 

 can continent, and he indorses the opinion of Mr. Darwin and 

 Mr. Ball that this absence is due to the fact that the only 

 country from which they could have been derived could not 

 supply species adapted to the soil and climate. As this is a 

 subject to which I paid considerable attention during a long 

 residence in South America, I venture to call attention to the 

 explanation of this phenomenon, which my observations gave 

 rise to as described in my " Visit to South America," 1878. 



The peculiar characteristics of these vast level plains which 

 descend from the Andes to the great river basin in unbroken 

 monotony, are the absence of rivers or water-storage, and the 

 periodical occurrence of droughts, or " siccos," in the summer 

 months. These conditions determine the singular character both 

 of its flora and fauna. 



The soil is naturally fertile and favourable for the growth of 

 trees, and they grow luxuriantly wherever they are protected. 

 The Eucalyptus is covering large tracts wherever it is inclosed, 

 and willows, poplars, and the fig, surround every estancia when 

 fenced in. 



The open plains are covered with droves of horses and cattle, 

 nil. I overrun by numberless wild rodents, the original tenants of 



