THE PREPARATION OF cl-GALACTURONIC ACID FROM LEMON PECTIC ACID.*

A noteworthy advance in the knowledge of the constitution of the pectic compounds was afforded through the excellent researches of Ehrlich and his coworkers (1)) who discovered that d-galacturonic acid, an isomer of d-glucuronic acid, was a constituent of all pectic substances so far examined. Later researches showed that the pectic acid obtainable from sugar beet pectin (2) can be regarded as a triacetyl-arabino-galacto-dimethoxy-tetragalacturonic acid, wherein the galacturonic acid comprises approximately 68 per cent of the molecule. Essentially the same structure was deduced for the pectic acid from flax pectin (3) which is made up of 61 per cent of galacturonic acid, and the pectic acid from orange peelings which is composed of 73.7 per cent of galacturonic acid. In 1924, the senior writer had occasion to require considerable quantities of galacturonic acid for biochemical studies conducted in conjunction with Dr. James G. Dickson of the Department of Plant Pathology. After considerable experimentation with the various commercial preparations obtainable and several prepared in the laboratory from sugar beet pulp and apple pumice, it was found that a lemon pectin preparation from the California Fruit Growers Exchange Laboratory afforded the most economical and convenient starting material. In view of the fact that the study of the chemistry of the pectin constituents (4) has recently attained a rather preeminent position in organic and plant biochemical