4S DENSlTItvS OK (iXVtiKN AND MYOROGKN 



reveisiil, after whifli l> was wanuetl ami fitted to the st(ii)cock of the globe. < *n e 

 was now Htteil the coiTespoiiding gnniiul joint /', and this was fused to tiie air 

 [nnn|). When tbe exhaustion was c()nipleted, (/ wjis closed Ity fusion, the part 

 fused off was removed from /', cleaned, and put on the balance with the glohe. 

 From the weight of the glass attached to the glol)e, together with tiie voliinu' be- 

 tween the key of tlit- stopcock and the point il, is computed tin- volume added to 

 Jie globe. The weight of the glass added is known from the pivliminary weigh- 

 in"; it of coui-se sim}>lv re[)laces a certain amount of brass ami platinum weights 

 which otherwise would liave been needed. The manner in which the .•iddition of 

 tliis voluiiu' was cared for is to be descril)ed in the next ]iaragi'apii. 



2\). — oxy(;en by second jiktiiod. courkction kou dikkeue.nck of volumes. 



In all the experiments of this series, the volumes suspended from the opposite 

 pans of the balance were made equal at every weighing. For tliis purpose, some 

 sixty minute flasks were made, of sizes ranging from one cubic centimetre to ten. 

 They were all made nearly equal in weight by loading with mercury, closed by 

 fusion, ami provided with platinum hooks. The appearance of 

 one is shown in Fit;. 21. Their volumes were then determined 

 by hydrostatic Aveighings and mai-ked on them by etching, after 

 Kk;. 21.— Small rtask wliicli they Were made rigoiously equal in weight when weighed 

 for equalizing volumes. j,j .^ vacuuui. Tliis was accomplished on an assay balance whose 

 needle moved fifty divi-sions for a difference of one milligramme, taking account 

 of the density of the air and of the errors of the Aveights employed. 



When the difference of volume of two ma.sses to be counterpoised against each 

 other had been determined, two of these minute flasks were selected, siicli that the 

 ilifference of their volumes was equal to the difference of volumes of tlu- iiias>es to 

 be weighed ; adding the small flask to the large volume and conversely, the 

 volumes to be weighed became equal. These flasks had been so accurately ad- 

 justed to e(pudity of w^eight in vacuo by i-epeated determinations that it was not 

 necessary to take account of their weight or of the minute differences of their 

 weights. 



As an example of the simplest application of the e([uating flasks, a joint, h e 

 Fig. 20, weighed appioximatelv 7.77 grammes, and had tiierefore a volume of ■'.11 

 cubic centimetres. The weights to lialainf it iiad a volume of 0.85 cubic centime- 

 tres. .\diling to these two \'>liiMies two flasks lia\iii^^ volumes of 1.11 .•iml '.''Xu^ 

 cubic centimetres, we have the two volumes on the opposite pans of tin- l)alaiice 

 .•'..1 I i\- + 1.41 cc = 4.52 cc, and 0.8") cc + 3.(>;j cc = 4.50 cc. 



Ill the case of an exhausted ulobe, the number of volumes to be added to- 



