Acids which have more than four substituents in the a or ß positions should be practically unesterifiable under ordinary conditions.12 Finally, if considerable substitution in the a or ß positions has already been made, substitution in the 7 position may have some effect on esterification rate.It has been demonstrated already that the effect of lengthening the alkyl chain of the acid portion of ethyl esters on the rate of saponification of these esters is the same as that observed in esterification.8 In a subsequent paper it will be shown that the general effect of a and ß substitution is the same for these two processes.(12) Cf. Braun and Fischer, Ber., 66B, 101 (1933).

A seri es of selected or specially prepared catalysts were s tud ied fo r t heir abili ty to accelerate the ortho to para conversion of hydrogen . The res ults of t hi s st ud y a re presented and the p erformance of vari ous catalyst s are compared with t hat of chrom ic oxide on al u: mina pellets. An outstandin g cata.lyst, u~s upporte d hydrous J erric oxide g ra nules, was selected for further study a nd used 111 the liquefi ers of t he NatIOnal Burea u of Standards Cr yogenic Engineering L aboratory. One and one-half liters of t his catalyst has now bee n used to convert more t han 100,000 li ters of liquid hydrogen to 90 to 95 perce nt pa ra at an average rate of abo ut 235 liters of liquid per hour. There is to date no ev id ence of decrea se in effici ency with continued use.

A new apparat us a nd technique, in whi ch vac uum pumps and assoc iated eq uipm ent are not required, have been developed for t he determinatiolJ of the a dso rption of nitrogen fr om mixt ures with he lium for use in t he determination of surface area. The sample is heated initiall y in a stream of helium. The adsorption of he lium is negligible at the temperatu res concerned. The gas mixture is cycled repeatedl y over the adso rbent until no flll'th el' change in press ure is observed. T emperature equi libration is attained rapidly. It is shown t hat t hermomolecular press ure differe nces are neg li gible under the conditions of t he experime nt . Surface-area determinations by t he s implified technique are in good agreement with resul ts obtained by t he con ventional volumetric method when the same adsorbents a re used with various residual helium pressures .

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