SCIENCE 



NEW YORK, MARCH 17, 1893. 



WHERE IS THE LITRE?— A MODERN SCIENTIFIC PUZZLE- 

 PICTURE. 



BY STEPHEN H. BMMBNS, YOUNGWOOD, PA. 



In Engineering News of Oat. 30, 1892, appeared an article on 

 Fuel-Gas Values, in which I gave a table entitled " Some Metric 

 Constants," designed to show the variations of value to be found 

 in the text-books even with regard to so fundamental a matter 

 as the volume of the litre. The publication of this table has 

 caused me to receive a letter of protest from my friend, Mr. 

 Latimer Clark, B'.R.S.. who, as all the world knows, takes rank 

 among the foremost living authorities on the subject of weights 

 and measures; his " Dictionary of Metric and other Useful Meas- 

 ures " being a permanent masterpiece. This letter contains much 

 that is interesting to the scientific world, as will be seen by the 

 following quotations which include all the material passages: — 



" I have looked over the varying list of values and it is not 

 very difficult to account for the discrepancies. Many of them 

 have taken the values as defined by Act of Parliament, and as 

 published by the Board of Trade. But all the world has known 

 for years past that this valuation is very far wrong, and therefore 

 the more careful writers have endeavored to correct the error as 

 far as they were able by using the best results they could obtain 

 or hear of. Some of them, however, are not quite so easily ex- 

 plained (S A. Ford, for example). 



" For the past thirty years no scientific writer or worker has 

 used the Board of Trade official value of the cubic inch of water, 

 viz., 253.458 grains. This is the simple cause of the discrepan- 

 cies you point out. You have been a little hard on me in the 

 matter, and your article would certainly lead any one to suppose 

 that I had given three different values tor the litre, which is 

 very far from being the case. After the book was all printed 

 ready for issue, the new Board of Trade measurements came out 

 and I rewrote and reprinted a great part of it in order to make it 

 conform to the new legal definition of the Board of Trade. Up 

 to September, 1891, I had always assumed the cube decimetre 

 and litre to be identical. ... At page 57 I call especial atten- 

 tion to the change, in the footnote, and again in the article 

 ' Water,' at page 90, and I give there a table of the volumes of 

 the litre and cube decimetre. Then, again, at page 103, I give 

 a special note on the capacity of the litre. I beg you to read 

 these with care, for it is evident thai you have read hastily and 

 have never put your back into tine question. If you had read 

 carefully you would have found abundant warning against con- 

 founding the litre with the cube decimetre. They are practi- 

 cally the same, and can be differentiated only by means of the 

 most costly apparatus used by the most skilful physicists and 

 with extraordinary precautions; but then you were writing from 

 a scientific point of view and you ought to have read carefully. 



''Then in reference to the 'cube inches into litres," page 47. 

 You ignore the six places of decimals given in the first column, 

 and pass on to the subsidiary column of reciprocals where only 

 two are given, and by some process you expand them into five 

 places of decimals, some of which are, of course, sure to be 

 wroug. Strangely enough, too, while going to this trouble, you 

 fail to notice that on this line and the one above it (' into cube 

 decimetres') the two figures are given differently, viz., 61.04 and 

 61.0270. This would certainly have caught your eye if you had 

 been really studying the question, but I fancy you were more 

 intent upon writing a rattling article for the press. 



"I hope you will find some opportunity of correcting the im- 

 pression that my book is not trustworthy, for it is at the present 

 day the only book that gives the English measures correctly. 



" I note that in the constants you have adopted, you use 

 38.3127 as giving the number of ' litres in a cube foot.' I do not 

 quite see what you take this from, but in England the number is 

 38.3110, while the number of cube decimetres is 38.3153. 



" In the United States the metre is by law = 39.37 inches, but 

 in England it is 39.37079 inches. From the latest measurements, 

 however, the U. S. number is likely to turn out more accurate 

 than the English number." 



In order that this letter may be clearly understood it is desir- 

 able to quote the published statements to which it refers. These 

 are as follows: — 



1. The reference fo Mr. Clark's book in my table appeared 

 thus: — 



Cu. inches in Cu. feet in Litres in 

 "Authority. 1 litre. 100 litres. 1 Cu. ft. 



Dictionary of Metric 



Measures, by 

 Latimer Clark, F.R.S. 61.0364 3.5333 38.3110 



Ditto 61,04 3.5333 28.3093 



Ditt6 (cube decimetre.) 610270 3.5S16 28.3153"' 



3. After directing attention to some current arithmetical in- 

 accuracies on the subject of the heat- value of natural ga?. I re- 

 marked as follows, in the paper concerning which Mr. Clark has 

 written me: — 



" Considerations of soaoe forbid my entering at further length 

 into the correction of published errors. Every careful matj who 

 has ever consulted a text-book will grimly admit the jiis'ice of 

 this remark; even though he may willingly agree with me in 

 sincerely thanking the Trautwines and Haswells and Gmelins 

 and Ciarks and Thomsons and Favres and Regnaults and Berthe- 

 lots, and all the brilliant compilers who have dene so much good 

 and worthy work in aiding the progress of knowledge." 



3. The foot-note at p. 57 of Mr. Clark's book is: — 



"The litre was designed to be the volume of a cube decimetre 

 of water in vacuo at maximum density, but is actually somewhat 

 greater. It is now understood as the volume of one kilogram of 

 water freed from air, at maximum density and weighed iu 

 vacuo. It is, therefore, dependent on the dimensions of the 

 kilogram and not of the metre. The litre used in these tables 

 has the capacity above defined; the equivalent weight of water 

 employed is not the kilogram but the actual vi'eight in air (see 

 ' Water")." 



4. The article " Water" at page 90 of Mr. Clark's hook is : — 



" The weight of the cube inch of water at 63° F., used in the 

 following table and throughout the work, is not the old and well- 

 known cubic inch of 353.458 grains, but the newer determination 

 by the Standards Department of the Board of Trade, viz., 1 cubic 

 inch of distilled water, freed from air, at 63° F., weighed in air 

 against brass weights, barom. 30 inch =352.28599 grains. This 

 measure has already been legalized. It is distinguished by the date 

 1890. The old weight of the cubic inch was legalized by Act of 

 Parliament in 1824, and when used it is distinguished by that 

 date. 



"The gramme of water is very commonly considered identical 

 with the cubic centimetre, and the kilogram is similarly taken as 

 equivalent to the cubic decimetre or litre, but these relations are 

 only true when they are weighed iu vacuo and at maximum 

 density, 4° C. The litre of water (1 kilogram in vacuo at 4° C.) 

 when weighed practically, that is, against brass weights in air, 

 barom., 30 inches, loses 16.5 grains, owing to displacement of 

 air, and then weighs at 4° C. only 998.93 grammes instead of 

 1,000. The difference is, of course, greater at ordinary tempera- 

 tures. In addition to this, the kilogram, and therefore the litre, 

 is supposed to be intrinsically heavier than the cubic decimetre 

 of water in vacuo by about 130 milligrams or 1.85 grains, owing 



