REVIEWS. 
many methods have been suggested whereby the cost might be reduced. These 
suggested methods fall into two groups— 
1. Those in which it is proposed to find commercial uses for the pear 
and thereby pay the whole or part of the cost of clearing the 
pear-infested land. 
2. Those in which it is proposed to utilize special machinery, poisons, or 
natural enemies to destroy the pear. 
Of the great number of ways suggested for utilizing the pear, the only one 
which has proved satisfactory is that of feeding it to stock. By the addition 
of various additional feeding stuffs satisfactory rations for cattle and “dry” 
sheep, consisting chiefly of prickly pear, can be provided. Breeding ewes and 
lambs, however, do not do well on pear. If all the cattle in Australia were fed 
entirely on prickly pear it is doubtful whether they would be able to keep pace 
With its annual increase alone, hence as a means of eradicating the pest from 
Australia its utilization for stock is not very helpful. ‘ 
The manufacture from prickly pear of alcohol, paper or cardboard, potash, 
and various other materials has been suggested, but in all these cases the fact 
that prickly pear consists very largely of water makes its profitable commercial 
utilization very unlikely. 
No satisfactory machine for destroying prickly pear has yet been invented, 
and the problem, owing to the bulk of the material, is a very difficult one. 
Greater success has been achieved in the search for poisons, and as a result 
of a very large number of tests it has been established that compounds of 
arsenic are the most useful poisons, being specially toxic to prickly pears. 
Arsenic acid is the most deadly compound for use in solution as a spray or by 
injection, but, unfortunately, it is practically unobtainable in Australia. 
Arsenious chloride is at present the chemical chiefly in use, and is applied either 
as a spray or in the form of gas where the pear is impenetrable. Arsenate of 
soda, being cheaper and less dangerous to handle, is still used to some extent, 
but necessitates the use of large quantities of water in making solutions, and 
at least two sprayings are required to kill the pear. 
Mechanical or chemical treatment necessitates continuous work of some 
kind for keeping the land clear The only method which has been suggested 
whereby the plant might ultimately be destroyed is “by the employment of 
natural enemies, and it is only by the introduction of such enemies that even the 
land which is now clear can be considered safe from further serious infestation. 
A large number of kinds of insects are known which feed exclusively on one or 
more kinds of prickly pear, and in the absence of pear cannot survive.- The 
only insects of this type yet introduced to Australia are certain wild cochineal 
insects which feed on the so-called tree pear (Opuntia monocantha), and in a 
few years they practically exterminated this variety of opuntia. It is hoped 
that the Institute of Science and Industry will be able shortly to take up this 
work. The Institute recently issued a bulletin (No. 12) dealing with this 
subject, which was prepared by Mr. W. B. Alexander, M.A. 
Asphalts and Allied Substances, by Herbert Abraham, B.Sc., D. Van Nostrand 
Co., New York, 1918. This treatise has been prepared for those interested in the 
fabrication, merchandising, and application of bituminous products, and em- 
braces—(1) methods serving as a guide for the works chemist engaged in testing 
and analyzing raw and manufactured products; (2) data for assisting the refinery 
or factory superintendent in blending and compounding mixtures; (3) informa- 
tion enabling the ambitious salesman to enlarge his knowledge concerning the 
scope and limitations of the articles he needs; and (4) the principles underlying 
the practical application of bituminous products for structural purposes, of 
interest to the engineer, contractor, and architect. Subject-matter of sole value 
to the technical man has been segregated under the heading, “ Methods of 
Testing,” excepting an outline of the “ Chemistry of Bituminous Substances.” 
The earlier chapters comprise an historical and geological review of the use 
and origin of bitumens and pyrobitumens, and the methods of refining. The 
section dealing with tars and pitches records the advances made in recent years 
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