
1913] BRIEFER ARTICLES 227 
inch beyond the twine should be trimmed off with a sharp knife (fig. 2, C). 
This trimmed membrane after further drying for an hour should then 
be kept in a dish of water until needed for use. MatHEws? dried his 
membranes over a steam coil for several days, but found that perfectly 
dry membranes did not allow the solute to pass through very rapidly. 
As considerable variation was found in membranes made in the 
same manner and at the same time, various attempts were made to 
' reinforce them and make their tensile strength more uniform. The 
method used for testing a membrane consisted in suspending the osmom- 
eter and then pouring mercury into the tube until the membrane broke, 
noting the height of the column of mercury in the tube at that time. 
Usually there was not a rupture of the entire membrane, but a small leak 
in one place, and that generally near the flange of the bulb. The differ- 
ent methods used in making the membranes, and their tensile strength, 
as indicated by the height of the mercury column, are shown in the table 
given below. 
TABLE SHOWING THE RELATIVE STRENGTH OF VARIOUS MEMBRANES 
The figures refer to the height (in cm.) of the column of mercury when the mem- 
brane broke. 

Methad of f, + rst ad 3d 4th sth Average 


Not oye bag in water 5 min. after 
Heine made... Se 13.5 B.6 | Yat0 [eee ass 11.33 
Not tied: le dried one hour, then : 
ek ite os oe, 10:5 |. 4.5 | 13.5 | 16.0 ]...... 10.39 
Membrane a with bar net- 
ee ie Re es ee os 17.0 14455 1 10 Pe cie< 16.17 
Not tied; Sine BE in chloroform 48 
ode ELMS AEP Eee OE OP Neo irs PrN bh a Be ees ee ae er a 14.17 
Double membrane; not tied........ 73.0 | 29.0 | 73.5 | 54.0 | 64.0] 58.70 
Single membrane, tied; air dried 24 
OU hs ae ee 9.0] 59.0| 11.0] 8.5 | 41.0} 25.70 
Same, then soa aked 24 hours in water. . 27.0 | 8.0] 62.0 | 52.0 | 22.0 | 34-20 
ae uble donee tied and dried in 
RSA aa any ee 94.0 | 36.0 |238.0 |230.0*/215.0*| 163.40 








* No break in the membrane occurred when the height of the mercury column had reached this 
int. 
As the above tests show, the double membranes are by far the 
strongest. These are produced by making a second single membrane 
and superimposing it over one made in the manner described above 
(fig. 2, D). There may be one or two bubbles of air between the two 
? MatuHeEws, J. H., Osmotic experiments with collodion membranes. Jour. Phys. 
Chem. 29: 281-291. 1910 
