The series of the normal saturated fatty acids and their methyl esters with 5 to 20 carbon chain atoms was synthesized and careful purified, mainly by fractional distillation of the methyl esters in columns with up to 58 theoretical plates. The purity was checked with the aid of melting curves determined in a microcalorimeter and proved to be 96.6% or better. Refractive indices were determined and can be represented by with an accuracy of 5 units in the fifth decimal place (c = number of carbon chain atoms). Densities, accurate to 1 unit in the fourth decimal place, can be represented by Boiling points can be given by b.pt. 20 mm for the methyl esters (c> 5), accurate to 0.1 °. From our data, combined with literature values, the molecular refractivity of the CH2 group in an aliphatic chain calculated according to Lorentz‐Lorenz. was determined at 4.64 at room temperature. In addition, melting and transition points, and heats of fusion and transition were determined.

Accurate heats of combustion of the title compounds were measured in an electrically calibrated calorimeter; the liquid samples were burned in Pyrex ampoules; the water content in the samples was titrated by the Karl Fischer method.The increment of the standard enthalpy of combustion, -AHgliq. (-1-AHeliq.) for one C H Z group in the chain proved to be 653.8 kjlmole for both the acids and the methyl esters studied, which is the same value as determined for the liquid paraffins. The following formulae, in which c = the number of carbon chain atoms (c > 5) can be used to calculate the standard enthalpies of combustion (based on the 1951 atomic weights): -AHgliq = 653.8 c -430.2 kj/mole for the acids, accurate to 0.03 -0.04%, -AHgIiq. = 653.8 c + 292.6 k j h o l e for the methyl esters, accurate to 0.02%. The theoretical heat of esterification of a fatty acid with methanol at 25 " C , disregarding heats of solution and dilution, was calculated to be 3.8 f 0.6 kj/mole, which can be compared with the value of 4.2 f 0.3 kj/mole for the theoretical heat of esterification of acetic acid with ethanol at about 20 "C, determined directly by Mme BPretiger-Calvet. Syntheses and purificationThe series of normal saturated fatty acids and their corresponding methyl esters with 5 to 20 carbon chain atoms were synthesized and carefully purified, as described in a previous paper 1.The impurity in the final samples was such (except for the water content, which was accurately determined) that its influence on the heat of combustion was less than 0.01 %. The water content was corrected for. Apparatus and procedureThe original calorimetric equipmentprovided with an isothermal jacketwas described in 1947 2 . Some minor alterations were made in * Full details can be found in the thesis of N. Adriaarise, Vrije Universiteit, Amsterdam (1960), which is available on request. N . Adriaatjse, H. Dekker and J. Coops, Rec. Trav. Chim. 83, 557 (1964).

The heats of combustion of some samples of pure benzoic acid, partly supplied by the National Bureau of Standards (Washington) and partly prepared by the authors, have been carefully measured by reference to electrical standards. The mean value of the absolute heat of combustion of benzoic acid under standard bomb conditions in some series of determinations carried out in the years 1946‐1948 is 26438 ± 4 j/g. New determinations in 1954 showed a mean value of 26435 ± 4 j/g.