high boiling points and refractive indices. These were probably ketone condensation products but no attempt was made to identify them because of the small quantities available.There were also indications that isomerization of alkylacetylenes involving migration of the triple bond occurred in contact with the catalyst. Thus the liquid products recovered from an experiment on butyne-1 (b. p. + 8°) contained a small quantity of material which may have been butyne-2 as it boiled at 25-30°, was insoluble in water, gave no reaction with semicarbazide hydrochloride, and turned red on contact with sulfuric acid, as is characteristic of butyne-2.The materials available were insufficient to show whether pentyne-1 and pentyne-2 isomerized into each other. It is probable that each of these may hydrate to the same ketone without isomerization.The fact that heptyne-1 hydrated to 4-heptanone is evidence that isomerization of this alkylacetylene occurred before hydration.The authors are indebted to Mr.

low-temperature (-1 96' C.) nitrogen adsorption-desorption isotherms have been measured on pure silica and a range of silica xerogels thermally modified from 240' to 1 1 0 0 O C. B.E.T. surface areas and pore distribution characteristics are reported for each material. Results indicate that thermal modification has a significant effect on the surface areas and distribution data, especially above 700OC. In the majority of cases, B.E.T. areas are greater than the equivalent cumulative data. A range of noncylindrical pores is indicated in each material. With the exception of Macroporous silica gel, both the adsorption and desorption branches of the isotherms can be used for pore volume and surface area distribution determinations. In the former case, the desorption branch of the isotherm seems to lead to more apt results.S I L I C A gels and silicas are widely used in industry, and a close understanding of the surface and bulk properties of such materials is of practical importance in the technology of cracking catalysts, catalyst supports, mineral processing, ceramics, and adsorbents. Such an understanding is, in addition, directly involved in the manufacture and use of siliceous fillers and thickening agents in organic systems, including paints, inks, elastomers, and lubricating greases.Recent studies have been reported of the sorption of ammonia ( 6 ) , ethylamine (23, 24), and sulfur dioxide (14) on silicas and silica xerogels of high purity. Surface and structural modifications were achieved by thermal treatments, largely in the range 240" to 1100" C. T o characterize the materials, a large number of low-temperature (-196" C.) nitrogen adsorption-desorption isotherms were determined.Low-temperature gas adsorption isotherms have been widely used in the past to evaluate the effects of heat treatment on silica gel and gel-like structures (1, 2, 3, 5, I O , 18, 21, 22), particularly by the application of the B.E.T. equations (5). The method was used here to characterize materials, with special regard to surface area. Additional detailed information on pore-size distributions has been obtained by applying the Cranston and Inkley method (7) to the isotherms. This method provides independent comparative surface area data (to the B.E.T. values) and can be applied to both the adsorption and desorption branches of the isotherms. The results were calculated on the assumption of a molecular cross-sectional area for nitrogen of 16.2 A.2 (the most frequently used figure). However, there have been suggestions that the quadrupole moment of nitrogen can interact with hydroxyl or other polar groups, leading to a change in cross-sectional area (19). In spite of this, nitrogen adsorption generally gives the most meaningful results in low-temperature adsorption studies.Results from the adsorption measurements and from the isotherms were analyzed with the aid of an Elliott 803 computer . EXPERIMENTAL Materials. The major portion of the study was carried out with Davison 923 chromatographic grade silica gel (> 99.98% pure). Its surf...