. American chemical journal . tion and the purpose of the different parts aresufficiently obvious, so that it is necessary only to call atten-tion to its weak points. The membrane, when once deposited on the cell wall, mustnot be subjected to any strain except that exerted directlyoutward by the osmotic pressure; in other words, it mustnot be disturbed by any of the operations connected withthe closing and opening of the cell. To avoid this, the glasstube, B, was rigidly fixed in the cell, A. The lower end ofthe glass tube was accurately ground to fit the soapstonering, b. In order to prevent
. American chemical journal . tion and the purpose of the different parts aresufficiently obvious, so that it is necessary only to call atten-tion to its weak points. The membrane, when once deposited on the cell wall, mustnot be subjected to any strain except that exerted directlyoutward by the osmotic pressure; in other words, it mustnot be disturbed by any of the operations connected withthe closing and opening of the cell. To avoid this, the glasstube, B, was rigidly fixed in the cell, A. The lower end ofthe glass tube was accurately ground to fit the soapstonering, b. In order to prevent the solution from penetratingthe cement above, and at the same time to protect the latterfrom liquid entering through the exterior wall, the glass tubeand the soapstone ring were joined together watertight bymeans of molten shellac, and the lower end of the tube andring, and also the whole wall of the cavity, were painted witha solution of rubber. The ring and tube were then pressed 1 This Journal, 34, 4. 268 Morse and Fig. I. Cells for Measurement of Osmotic Pressure. 269 into place, and the space between the former and the cellwall was filled with the dissolved rubber, after which therubber lining was hardened by baking at a temperature be-low the melting point of the shellac. Finally, the spaceabove the ring was filled with the litharge-glycerine cement. So far as securing a rigid union of glass tube and cell isconcerned, the method proved to be perfectly satisfactory;but two difficulties developed, either of which made necessaryan occasional reopening and renovation of the cell, and these,as explained in a former paper, ^ are tedious and often un-successful operations. After a few months of use, the cellwas sure to fail in consequence of a peeling of the rubberfrom some of the parts protected by it. Again, the mem-brane becomes, in the course of time, so dense and thickthat the passage of water through it is intolerably slow, andit is necessary then to remove it and
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