272 PROCEEDINGS OF THE AMERICAN ACADEMY. 



irregular as that observed in the case of the hard Jena glass, dis- 

 crepancies in the compressibility determined with the same piezom- 

 eter of as much as 3 per cent are to be expected, at least over any 

 considerable pressure range. Doubtless this uncertain correction for 

 the envelope is the cause of the discordant results previously obtained. 



The work of Amagat and de Metz along this line seems the most 

 credible. Each gives the mean of the results with several piezometers, 

 where others have used. only one. The results of de Metz 4 with 

 four piezometers vary as much as 5 per cent, while those of Amagat 5 

 with seven piezometers vary 2 per cent. The value of Amagat at 20° 

 is 0.00000380 kgm./cm. 2 while that of de Metz is 0.00000379 kgm./cm 2 . 

 Lately Richards 6 obtained the value 0.00000371, working with a glass 

 piezometer by an electric contact device, but in such a fashion as to 

 eliminate the necessity for calculating the compressibility of the glass, 

 this step being replaced by a calculation from the observed linear com- 

 pressibility of steel, in which large percentage errors are of much less 

 importance. The values above are for a small pressure range: de 

 Metz and Amagat 50 kgm., and Richards 500 kgm. The results all 

 agree within a unit in the last place, when correction is made for the 

 difference in pressure range. 



The only work over a wider range seems to have been done by 

 Carnazzi,7 who worked between and 200° and went up to 3000 

 atmos. He used a glass piezometer, assuming Amagat's mean value 

 for the compressibility of the glass, and a manometer depending in 

 a way not entirely free from objection on the compressibility of water 

 as determined by Amagat. Only two significant figures are given in 

 the results, compressibility at 23° being 0.0000038 from to 500 atmos., 

 and 0.0000034 from 2500 to 3000 atmos. These results must be de- 

 creased about 3 per cent, becoming 0.0000037 and 0.0000033 re- 

 spectively, to reduce from atmospheres to kilograms. 



In the present determination, a steel instead of a glass envelope 

 was used. The advantages of a steel over a glass piezometer are mani- 

 fold. The correction for the compressibility of the steel is only 15 

 per cent of the total effect against GO per cent when glass is used. 

 Again, the steel is very much more regular in its elastic behavior than 

 the glass; this is obvious at once from an inspection of the curves 

 showing the compressibility of the glass and of the steel. It has been 

 already stated that the irregular behavior of the glass might introduce 



4 de Metz, Wied. Ann., 47, 706 (1892). 



5 Amagat, C. R., 108, 228 (1888). 



6 Richards, loc. cit.. p. 51. 



7 Carnazzi, Nouv. Cim., 5, 180 (1903). 



