PRO-PHYSICAL AND CHEMICAL PROPERTIES OF ING BRICK CLAYS.
Relations—In the discussion of the physical properties of clays it was shown that there is a possibility of making some correlations between the several physical factors. It was also demonstrated that the physical properties affect the adaptation of clays to processes of manufacture. No relation was found to exist between the chemical composition and working properties, so no attempt was made to correlate the chemical and physical properties.
We are now to consider those properties of clays which are manifested in the process of burning, and it is here that we should be able to trace the combined effect of the physical and chemical properties. In burn ing, the physical and chemical properties of raw clays surely operate as causes having as effects the pyro-physical and pyro-chemical proper ties. If, knowing the physical and chemical composition of the raw clays and the pyro-physical and chemical effects produced in burning, we are not able to trace a logical and invariable sequence between the causes and effects, we will be forced to admit: either (a) That accord ing to the data at hand, clays having similar physical and chemical properties in the raw state, may behave differently in burning, or, (b) That it is at present impossible to determine exactly the physical and chemical condition of raw clays; or, (c) It is impossible to trace the effect of individual physical and chemical properties where so ,large a number of changes occur simultaneously; or, (d) That, reasoning from analytically determined causes to observed effects is an absurdity if the evidence does not permit of a reverse reasoning, i. e., from effect to cause.
The first case, that of clays of similar character behaving differently in burning, is forcibly illustrated in the case of fire clays. Fire clays, having similar ultimate chemical composition and size of grain, may have radically different pyro-physical behavior. The one may burn to an open porous mass at cone 11, being fit for fire brick purposes; the other may burn quite dense at cone 8, being fit for stoneware, sewer pipe, etc. This fact was noted in the preliminary report on fire clays,' and
will be illustrated in this report under the tonic "Changes That Take Place During Fusion." The second case; the impossibility of determining exactly the physical and chemical condition of raw clays, is illustrated by the fact that in the more exact of the two analyses, the chemical, chemists do not claim to be able with ordinary care and attention to details, to determine all of the elements that may be in a clay, nor do they claim to be able to determine the combinations in which these elements exist.
The third case, or the impossibility of tracing the effect of several changes in physical and chemical conditions which take place simultan eously, is a well recognised fact. On a rectangular coordinate diagram, two changes; on a triangular coordinate diagram, three changes in properties can be traced with accuracy. No simple' method has yet been devised by which the effect of changes in four factors can he traced, and it is certainly beyond the capacity of the human mind to follow the effects of four or more changes, if they cannot be plotted diagrammatically. In the case of several clays, no two of which agree exactly in their -several properties, and in all of which there are a great many properties peculiar to the individual clays, it is beyond our ability to satisfactorily follow even all the known details. Broad generalizations with numerous and well-known exceptions are the best that experimenters have been able to make from synthetical mixtures of fairly pure clays. It is obvious, therefore, that with a heterogeneous assortment of impure clays, conclusions concerning the relation between the causes (the physical and chemical properties of raw clay) and ef fects (the pyro-physical and chemical properties) cannot he other than broad generalizations.