AN IMPROVED DENSITY GRADIENT TECHNIQUE AND ITS APPLICATION TO PAPER AND CLOTH ASH.

This article discusses a study which examined the application of the density gradient tube method to the identification of cloth and paper ash. The use of comparison gradient tubes, each of which contains one of the samples being compared, requires that the gradients be established so as to be as nearly identical as possible. This necessitates that each of the various liquid levels be added to heights which are very precisely identical. This is made difficult by drainage of liquid from the walls after adjusting each meniscus. Also, the addition of each of the liquid increments to each tube by pipet is slow and causes inhalation of vapors which is disagreeable and possibly detrimental to health. In the study, the samples were not weighed as has been customary with soil and other heterogeneous samples. An alternative which was essentially as satisfactory and much more rapid was to construct a small scoop which could be loaded quite reproducibly. Into each gradient tube was placed one scoopful of tube sample, thus approximating a uniform volume rather than a uniform weight of the various samples. It was found quite simple to reproduce the appearance of duplicate samples of the same ash, while the differences between different ashes was in no way affected.