August 13, 1903] 



NATURE 



347 



hands of the Secretary of State in prescribing a 

 standard of sufficient ventilation for factories and 

 workshops based upon what it deems to be an 

 adequate objective criterion of what constitutes reason- 

 ably " sufficient " ventilation, viz. the proportion of 

 carbonic acid in the air. Looked at from the point of 

 view of the Inspecting Department of the Home Office, 

 it was necessary, at the outset, to determine whether 

 it was practicable to make use of this proportion as 

 a legal standard of " sufficient " ventilation, or 

 whether such estimations, if made with the requisite 

 accuracy, might not prove to be both expensive and 

 troublesome. 



Determinations of atmospheric carbonic acid are 

 mainly carried out on the principle first made use of 

 by DaJton and worked out by Hadfield, that is, absorp- 

 tion of the carbonic acid contained in a known volume 

 of the air by a suitable alkaline solution, the amount 

 -o absorbed being ascertained by volumetric analysis. 

 This process was first extensively applied by Petten- 

 kofer, and is generally known by his name. With 

 proper precautions it is capable of a very high degree 

 i>f accuracy, and, indeed, practically all our know- 

 ledge concerning the distribution of carbonic acid in 

 ihe atmosphere, whether in the free air or in inhabited 

 places, has been obtained by its means. The apparatus 

 needed is somewhat bulky on account of the necessity 

 of using large volumes of air in cases where the 

 amount of carbonic acid is relatively small, as in 

 ordinary atmospheric air. At the same time, when 

 it is merely necessary to determine whether the air 

 of an inhabited room or that of a factory or workshop 

 contains an excess of carbonic acid over the quantity 

 that could reasonably be prescribed as an official limit, 

 vessels holding a couple of litres would suffice for most 

 purposes. It would be readily possible to put together 

 lor the use of inspectors a Pettenkofer " kit " which 

 >hould be light and not too bulky, and would enable 

 the estimation of carbonic acid to be carried out rapidly 

 and with approximate accuracy. 



The committee recommends' mf^r alia that the limit 

 of carbonic acid should be fixed, except on very foggy 

 days, when no tests should be made, on account of 

 the vitiated state of the outside air, at 12 volumes of 

 carbonic acid per 10,000 of air, and that when gas 

 or oil is used for lighting, the proportion should not 

 exceed 20 volumes after dark or before the first hour 

 after daylight, the only exception to this rule to be 

 in cases where the extra carbonic acid is produced in 

 other \ya)'s than by respiration or combustion, as in 

 breweries, &c. It is further recommended that 

 arrangements be made by the Factory Department of 

 the Hoinc Office for the analysis, by a specially quali- 

 fied person or persons, of samples of air colle'cted by 

 inspectors, and that any analysis on which a prosecu- 

 tion immediately depends should have been performed 

 by such qualified person or persons, and also that 

 arrangements should be iriade for inspectors of 

 factories to have the use, when desired, of a properly 

 tested portable apparatus for estimating on the spot 

 the proportion of carbonic acid in air. 



Dr. Haldane has devised an apparatus for the use 

 of inspectors of factories, a specimen of which has 

 been submitted to us for examination by Messrs. 

 Miiller, Orme and Co., of 148 High Holborn, and this 

 seems to fulfil all the necessary conditions. A descrip- 

 tion of it constitutes appendix iii. of the report before 

 us. The estimation of carbonic acid is made by 

 measuring the contraction in the volume of the air 

 to be tested by bringing the air in contact with a 10 

 per cent, solution of caustic potash or soda. As the 

 volume of the air taken for the test is only about 20c. c, 

 it is evident that special provision needs to be made, 

 and great care in manipulation needs to be exercised 

 if even approximate accuracy is aimed at. It is im- 



NO. 1763. VOL. 68] 



possible in the absence of the diagrammatic represent- 

 ation of the apparatus which accompanies the report' 

 to explain the details of its construction, or to make 

 clear the successive steps in its manipulation. We 

 have had, however, an opportunity of making a 

 number of experiments with it, and we are able to 

 state that the amount of carbonic acid in the air of 

 an inhabited room may be quickly ascertained, with 

 sufficient accuracy, by means of it. An intelligent 

 manipulator who understood the scientific principles 

 involved would be able to obtain results accurate to 

 within about one part in 10,000 with air containing 

 ordinary proportions of carbonic acid, and to about 

 two parts with air so highly vitiated as to contain, 

 say, from 30 to 50 volumes of carbonic acid per 10,000. 

 A trained gas analyst would, no doubt, obtain more 

 accurate results. A determination is made in a few 

 minutes when once the apparatus is put into working 

 order. 



Whether experiments of this kind should be entrusted 

 to those factory inspectors who have had no training 

 in physical science is perhaps open to question. 



One possible source of considerable error was in- 

 dicated during the experiments. After standing 

 several days the potash solution used in the apparatus 

 was found to be coloured yellow, doubtless from the 

 action of the alkali upon the rubber tubing of the 

 apparatus. Any sulphur thus dissolved would form 

 alkaline sulphides which would absorb oxygen from 

 the air under experiment, and so vitiate the result. 

 As a matter of fact, the figures given when the 

 apparatus was in this condition were wholly untrust- 

 worthy. 



The following experiments may bfe cited in illus- 

 tration of the degree of accuracy w^hich may be 

 obtained ; — 



I. Experiments on the air of a laboratory. 



Results. 

 COo per 

 10.000 of 



1st experiment. — At about 9. 45 a. m. , before 



any burners were lighted S'"^ 



T, f 2nd. About twenty minutes later 5 '9 



2or3Bunsens , ' „ than 2nd 6-3 



burning durmg^jj^ ^^ ^_ ^^ 3rd 7., 



the whole Ume ^ ^jj^ ^^ ^^ 4th 7*0 



oftheseexperi- gj^^ _^ ^_ ^th 7.4 



ments. \^^^^ ^^ ^^ ^^ ^^ _ 6th 80 



II. With air containing 2\- /^ volumes of CO^ per lo.coo. 



1st experiment ... 23 3 



2nd „ 217 



III. With air containing 45-2 volumes CO^ per 10,000. 



1st experiment 42'3 



2nd „ 4i"6 



GRXHAU BELL'S TETRAHEDRAL CELL KITES. 



IN the June number of the National Geographic 

 Magazine is a very interesting and instructive 

 article by Dr. Graham Bell on the tetrahedral principle 

 in kite structure. The article itself is so concise, and 

 depends so much upon illustrations which are repro- 

 duced to the number of twenty in the text and 

 seventy in an appendix, that an effective representa- 

 tion of the contents in an article of smaller dimensions 

 is scarcely possible. Still the line of thought that runs 

 through the work which the article represents is sa 

 clear and so suggestive that even an imperfect outline 

 of it may be useful. Dr. Bell indicates certain stages 

 in the development of his ideas as " milestones " ot 

 progress, and since the ultimate stage of the develop- 

 ment is the possibility of building up very large kite 

 structures by combining unit cells in such a way that 

 the proportion of weight to wing area in the structure 



