Wyatt recommends that two grams of the fine material be heated in ground watch-glasses, the edges of which are separated so as to allow the escape of the moisture.[14] The heating is continued for three hours at 110°, the watch-glasses then closed and held by the clip, cooled in a desiccator, and weighed. This method is excellent for very hygroscopic bodies, but where quick-acting balances are used, scarcely necessary for a powdered mineral. The residue from the moisture determination is gradually heated to full redness over a bunsen, and then ignited over the blast-lamp. This operation is repeated after weighing until a constant weight is obtained. The loss (after deducting the percentage of carbon dioxid as found in another portion) may be taken as water and organic matter. This method is sufficient for all practical purposes; but when minerals containing fluorin are strongly ignited, a part of the fluorin is expelled; hence, if more accurate determinations are required, the loss of fluorin must be taken into account. In this laboratory it has been proved that a pure calcium fluorid undergoes progressive decomposition at a bright red heat with formation of lime. Wyatt directs that the combined water and organic matters be determined in the residue from the moisture estimation as follows: The residue is brushed into a weighed platinum crucible, which is heated over a small bunsen for ten minutes and then brought to full heat of a blast-lamp for five minutes. After cooling, the total loss is determined by weighing. After deducting the carbon dioxid determined in a separate portion, the residual loss is regarded as due to combined moisture and organic matter. =25. Carbon Dioxid.=—Many forms of compact apparatus have been devised for this estimation, but none of them is satisfactory if accurate results are desired.[15] Not to mention other objections, many phosphates must be heated nearly to the boiling-point with dilute acid to effect complete decomposition of the carbonates. The distillation method described by Gooch[16] is excellent, and when once the apparatus is set up, its work will be found to be rapid and satisfactory. Wyatt regards the estimation of carbon dioxid as one of the most important for factory use. The carbonates present in a sample indicate the loss of an equivalent amount of acid in the process of conversion into superphosphate.[17] The apparatus employed for estimating carbon dioxid may be any one of those in ordinary use for this purpose. The principle of the process depends on the liberation of the gas with a mineral acid, its proper desiccation, and subsequent absorption by a caustic alkali, best in solution.