August 23, 1900] 



NA TURE 



387 



In the definition of the Marsupials, exception must 

 be taken to the statement that the young are always 

 nourished in a pouch ; and when mentioning the occur- 

 rence of the group in America no reference is made to 

 Ciienolesies. Indeed, the account of the whole group is 

 entirely inadequate ; and when the author speaks of the 

 value of American opossum fur, we strongly suspect he 

 had in his mind the product of the so-called opossums 

 of Australia. 



Finally, when treating of the Monotremes, the author 

 -tates that the spiny anteaters are represented solely by 

 llchiihia hystrix and E. setosa. As a matter of fact, 

 these two forms are but local races of a single species 

 whose name is E. aculeata ; and the author appears to 

 be totally unacquainted with the very distinct genus 

 commonly known as Proechicina ! 



As already said, we do not intend to criticise in detail 

 the nomenclature employed ; but in the retention of 

 names now discarded by those who have made a special 

 study of the class the author has done his best to put 

 his work out of touch with the present state of science. 



In making this statement, we are aware that the author 

 lays stress on the circumstance that he is treating his 

 subject from a biological standpoint. This, however, in 

 our opinion, is no excuse for neglect of the details o 

 classification and nomenclature. 



When treating of the adaptation of animals to their 

 environment, the author is always interesting ; and the 

 paragraphs devoted to this part of the subject are, to 

 our mind, the best in the whole fasciculus. R. L. 



GOOD AND BAD AIR. 

 The Carbonic Anhydride of the Atmosphere. By Prof. 

 E. A. Letts, D.Sc, Ph.D., and R. F. Blake, F.I.C., 

 F.C.S., "Scientific Proceedings of the Royal Dublin 

 Society," vol. ix. (N. S.), Part ii. No. 15. Pp. 270. 

 (Dublin : 190D.) 



The Air of Rooms. By Francis Jones, F. R.S.E., F.C.S. 

 Pp. 59. (Manchester : Taylor, Garnett, Evans and 



Co., I9CX3.J 



''pHE first of these pamphlets wouldamply justify its pub- 

 J- lication, if it only served to emphasise the necessity 

 of further investigation into the methods of estimating 

 carbon dioxide in the atmosphere. It is partly experi- 

 mental, partly bibliographical in character. The authors 

 finding themselves called upon to make a series of obser- 

 vations on the carbon dioxide of the air, have made a 

 careful study of Pettenkofer's method, and have intro- 

 duced some necessary corrections, without detracting 

 very much from its simplicity. They take the precaution, 

 suggested by other observers, of preventing the action of 

 the baryta solution on the glass by coating the vessel 

 with a layer of paraffin wax. It may be pointed out that 

 a solution in benzene is more suitable than the melted 

 wax. The thinner film obtained with the solution is less 

 liable to crack. The baryta solution is manipulated very 

 ingeniously out of contact with air. Yet with all these 

 precautions the results show that perfection is far from 

 being attained 



In the set of analyses on page 132 there is a dis- 

 crepancy between the highest and lowest figures of 10 per 

 NO. 1608, VOL. 62] 



cent.^ in another set on the same page the difference 

 anriounts to 17 per cent., and on the next page to 20 per 

 cent. 



It seems superfluous to introduce the third decimal 

 into the result when the experimental error affects the 

 first decimal place, and equally unnecessary to make a 

 correction for aqueous vapour, which only amounts to 

 about one and a half per cent, on the volume of carbon 

 dioxide, as against 10 per cent, or thereabouts from 

 experimental error. 



The authors omit to mention how long the baryta 

 remains in contact with the sample of air. This is an 

 important factor which should not be neglected, for there 

 can be no doubt that the absorption of carbon dioxide by 

 the baryta proceeds at a rapidly decreasing rate and 

 that the final traces of the gas may take many hours to 

 disappear. 



The book is full of useful information, drawn from a 

 variety of sources, the collection of which must have 

 cost the authors no little trouble. At the same time, one 

 is inclined to think that the value of the information 

 would have been enhanced if they had gone another step 

 and made a critical selection from the mass of analyses 

 which they reproduce, for the figures cannot all be equally 

 trustworthy, and many of them must be entirely illusive. 



The second pamphlet relates to domestic hygiene. It 

 treats of the effects produced on the air of rooms by the 

 use of gas, coal and electric light for heating and lighting 

 purposes. The effect is determined by estimating the 

 amount of carbon dioxide by Pettenkofer's method, and 

 by exposing a layer of permanganate solution to the air 

 and finding the quantity of the salt reduced. 



Mr. Jones, unlike the authors of the previous pamphlet, 

 is not troubled by misgivings about Pettenkofer's method, 

 except in the matter of the baryta attacking the glass. 

 He therefore substitutes lime-water as the absorbent, 

 apparently unaware of the fact that its effect on glass is 

 precisely of the same character, which may be easily 

 observed by placing very dilute lime-water coloured 

 with phenolphthalein in any glass vessel ; in a 

 day or two the colour will be completely dis- 

 charged. As the results here are only required 

 for comparison, great accuracy is not requisite, and the 

 ordinary method may be relied on. The results of the 

 permanganate method will scarcely serve to recommend 

 i It. We find, for example, that in two experiments made 

 on July 21 two-thirds the quantity of permanganate was 

 reduced in the one case in double the time. As Mr. 

 Jones points out, the quantity of dust may affect the 

 rapidity of reduction. If this is the case, effective ventila- 

 tion will produce disturbance of the air and movement of 

 dust as well as local currents from gas-jets, and it will be 

 difficult to differentiate the two. The results which Mr. 

 Jones obtains are precisely what might be anticipated if 

 we take into account the fact that a coal fire produces an 

 enormous air current through a room near the floor level, 

 whereas a gas fire usually only serves to carry away its 

 own products of combustion. Mr. Jones finds that the 

 purest atmosphere is maintained with a coal fire and 

 electric light ; then follow gas fire with electric 

 light, coal fire and gas light, and gas fire and gas light. 

 The worst effect is produced by an open gas cooking 

 stove without fliie. The author shows, moreover, that 



