84 FLORIDA GEOLOGICAL SURVEY-15TH ANNUAL REPORT

 Titanium-Titanium is often regarded as an uncommon constituent of clays but in reality it is of frequent occurrence. Rutile and ilmenite are the most important sources of titanium dioxide in clays. Unfortunately tests for titanium are rarely made in a chemical analysis. It exerts a blue and yellow coloring effect and Res has shown that it lowers the refractoriness of clay. Veatch2 states that titanium was shown in the analysis of some Georgia clays, but when those clays were examined microscopically no titanium minerals could be identified with certainty.
 Water-This includes the mechanically combined water or moisture and the chemically combined water. The mechanically combined water is that held in the spaces between the clay particles by capillary action and can be driven off by heating the clay to the boiling point of water. The loss of this water causes the clay -to shrink to a certain extent. This shrinkage, known as air shrinkage, ceases when the clay particles have all come in contact. The chemically combined water exists in combination with other elements and can only be driven off at a temperature ranging from 4000 to 600* C.
 Organic Matter-Organic matter, usually in the form of vegetable particles, occurs in many clays. It is a strong coloring agent in the unburned state and imparts to the clay a gray, blue, brown or black color. The same clays may, on burning, be red, buff, cream, or white, depending upon the other coloring agents. In such cases the carbonaceous matter has masked the other substances like iron in the raw state.
 Carbon may interfere with the proper oxidation of iron and expulsion of sulphur when present. Clays with a high content of organic matter are of common occurrence in Florida.
 It has been shown by the experiments of Orton and Griffin3 that between 800* and 900* C. is the best temperature interval for burning off the carbon, as below this the oxidation of it does not proceed as rapidly, and above this there is danger of vitrification beginning and the oxidation being stopped. All the moisture should first be driven out of the clay, then the heat raised as rapidly as possible to a temperature between 8000 and 900* C. and held there until the ware no longer shows a black core denoting ferrous iron.
 1Ries, H., Clays, Their Occurrence, Properties and Uses, p. 104, 1908.
 2Veatch, Otto, Clay Deposits of Georgia, Georgia Geol. Survey, Bull. 18, p. 48, 1909.
 3Second Report of Committee on Technical Investigation, National Brick Makers' Association, Indianapolis, 1905.