144 Prof. D. MendeleefF. On the Weight of a Cubic [Dec. 5, 



+0*27 gram, and as the water used was not sufficiently pure (having 

 a density of about 1"0005), the above-named result is to be considered 

 as of small accuracy and doubtless much in excess of its real weight. 

 Nevertheless, from these determinations, assuming the density of the 

 water used by Shuckburgh* to be as above mentioned, one may con- 

 clude that the probable weight is 1000*06 + 0*14 grams, which comes 

 very near to the real weight of the cubic decimetre, the small differ- 

 ence arising in all probability from the insufficient accuracy of the 

 temperature measurements near 62° F., at which the weighings were 

 made. 



It is well known that at the institution of the metrical system 

 at the end of the eighteenth century, the weight of the kilogram was 

 declared to be equal in vacuo to the weight of a cubic decimetre of 

 water at its maximum density. For this purpose M. Lefevre-Gineau 

 made an exhaustive investigation, upon which M. Tralles made a 

 report on the 31st May, 1779 (le 11 prairial, an 7), first published in 

 ' Base du System e Metrique,' Tom. Ill, pp. 558 — 580, in the year 

 1810 ; the original observations of Lefevre-Gineau are, however, 

 still unknown. From the data given in Mr. Tralles' report M. 

 Broch found in 1873f, after making the necessary corrections, that 

 the probable weight deducible from the data of the experiments lies 

 between the limits from 999'913 to 999*947 + 0*020 grams. I have 

 myself made a new reduction! of the data given by Tralles and Gineau, 

 the result being 999*966 + 0-03 grams. But to this result also we 

 cannot attribute any particular importance, principally for the three 

 following reasons : — 1. The original observations of Lefevre-Gineau 

 are unknown. 2. The cylinder employed by Lefevre-Gineau in the 

 numerous (altogether forty-eight) weighings at +0°'3 C. had a 

 special small tube providing a communication between the inner 

 part of the cylinder and the outer air ; there existed consequently 

 on the inner walls of the cylinder a condensation of aqueous vapour. 

 3. No particular indications are given as to the methods of purifying 

 the water in which the weighings were made, but considering the 

 fact that water once distilled without special precautions (as an ex- 

 periment shows) very often has a specific gravity up to 1*0002, 

 taking that of pure water as unity, we may admit that the true 

 weight will be smaller than that obtained from Lefevre- Gineau 's 

 investigations. 



From the above-mentioned determinations we must conclude that 

 the weight of a cubic decimetre of water in vacuo at 4° C. is not 

 greater than 999*96 grams, and hardly smaller than 999*76 grams. 



Of all the determinations made during the present century only 



* Shuokbnrgli, ' Phil. Trans.,' 1798, p. 155. 



f ' Proces-verbaux d. Comite international,' 1873 — 1874, pp. 122—140. 

 % For details see footnote j, page 143. 



