A STUDY OF THE CLEARING OF ALCOHOLIC PLANT EXTRACTS

Clearing is generally a necessary part of the analytical procedure with plant materials preserved and extracted with 80 per cent. alcohol, as advocated in a previous paper (3). Clearing is equally necessary when samples, killed and preserved by drying, are not given a preliminary extraction with ether before extracting with alcohol. The work reported here suggests that this necessity is based more upon the mechanical removal of lipoids, waxes, and certain colloids not precipitated by 80 per cent. alcohol, than upon the chemical removal of copper reducing substances. It is probable that comparable, although somewhat high, reducing-sugar values may be obtained with certain alcoholic plant extracts without either preliminary ether extraction or clearing. On the other hand, the alcoholic extract from fresh mangel leaves so clogs the filter, when evaporated and taken up in water, as to be unfilterable by ordinary means. The same is true of a large number of leaf, green-fruit, and woody-stem extracts. Correspondence with a number of physiological chemists indicated a lack of uniformity in clearing methods. A number of men were using neutral and basic lead acetate interchangeably although the work of BRYAN (1) indicates the danger of such a procedure. With these conditions in mind we have attempted to determine the limits of value and safety in the use of neutraland basic-lead-acetate solutions for clearing plant extracts-