. Archives of physical medicine and rehabilitation . cuum regulator. Asnoted in Section 54 below, a tube hard-ens when in use because of the adsorp-tion of gas by the glass walls, the metalelectrodes and possibly the regulatingsubstance itself. The hardening be-cause of method (2) simply means thatthis absorbing process increases withtime. In the case of regulators contain-ing some hygroscopic substance such asasbestos packing, method (3) has beenused with success by Levy and workers have shown that withsuch regulators, tubes may be conven-iently hardened by cooling the regula-tor
. Archives of physical medicine and rehabilitation . cuum regulator. Asnoted in Section 54 below, a tube hard-ens when in use because of the adsorp-tion of gas by the glass walls, the metalelectrodes and possibly the regulatingsubstance itself. The hardening be-cause of method (2) simply means thatthis absorbing process increases withtime. In the case of regulators contain-ing some hygroscopic substance such asasbestos packing, method (3) has beenused with success by Levy and workers have shown that withsuch regulators, tubes may be conven-iently hardened by cooling the regula-tor by means of an ethyl chloride exact details of using this method,which is extremely simple, the readeris referred to the original article. 1 hemethod is based on two sound scientificprinciples, (a) Water vapor in an en-closed vessel will condense until it hasthe equilibrium pressure correspondingto the lowest temperature of any pa iof the vessel. In this case the regulatortube becomes coated with snow andice. (b) The adsorption of gas, at. least in the case of many substances,increases with decreasing workers when using apparatusin which a high vacuum is necessary,frequently attain the required low pres-sure by attaching to their apparatus atube containing cocoanut charcoal im-mersed in liquid air. At the low tem-perature of liquid air the absorption ofthe charcoal is very great. It is desirable, however, to have atube too hard rather than too soft, for,as noted above, the remedy for toogreat softness is re-exhaustion. In this connection attention may becalled to an article by Mutscheller inwhich he describes a gas tube with asomewhat new type of regulator. Tobegin with, use is made of a new sub-stance which consists of a mixture ofnitrides of metals such as thorium,aluminum, barium, etc., and, it isclaimed, has the property not only ofliberating nitrogen when warmed by adischarge in the usual way, but also ofabsorbing or adsorbing nitrogen fromit
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