bearing trees are now being cultivated in the more easily inhabitable portions of the tropics, it will be a long time before this source of supply is an important factor in the market. And thus it comes that the synthesis of india rubber presents to-day, from at least the technical side, one of the most promising problems in chemistry.
The investigation of india rubber is greatly handicapped by the fact that it exists only in the colloidal state. The difficulties are perhaps more largely physical than chemical; that is, it is the molecular aggregation rather than the atomic structure of the individual molecule which presents such almost insurmountable difficulties. There are no clearly defined melting points, boiling points, tendencies to crystallize or any of those means of separating mixtures or characterizing individuals which aid in the investigation of most organic compounds. The researches of Weber and Harris, resulting in the establishment of the much needed methods of analysis, have been of incalculable advantage to all those working with either the raw or the manufactured article. In many directions also the paths along which important results are to be obtained have already been blazed by these investigators. Probably no other field presents such difficulties of manipulation in addition to such profound problems of organic chemistry as does the investigation of india rubber; but on the other hand few such unlimited opportunities for valuable work are offered in the field of chemical research.
Under the general head of utilization of trade wastes may be considered a large number of technical problems the solution of which would not only add wonderfully to the economic resources of the country, but would aid in the solution of that much vexed question, river pollution. We have already mentioned the soda and sulphite liquor resulting from the manufacture of cellulose fiber from wood. Of almost equal importance is the waste yeast which is daily produced in the brewing of beer and ale. An extract of this yeast has a food value as shown by analysis equal to the best meat extracts. As the quantity of yeast allowed to go to waste is from one to two pounds for every barrel of beer brewed, we can form estimates of the great amount of this material at hand. Arsenic sulphide from the purification of crude acids, grease from the washing of wool, the utilization of city garbage and many other problems of this order are everywhere in evidence. It is not within the compass of this discussion to mention these almost innumerable sources of manufacturing waste which exist in the chemical industry; but keen competition on the one hand and the state boards of health on the other are constant stimuli to increased effort towards their utilization.
Although I have endeavored to select the above examples of unsolved problems with a view to touching upon as large a portion of
