452 
NADORE 
| Marcit 7, 1907 
searches. On the other hand, the professed physicist, 
interested in the properties of matter from a more general 
point of view, prefers to work on materials of a more tract- 
able nature than those with which the geologist is concerned. 
The memoir before us, the joint work of a geologist and 
an engineer, deals with the constants of elasticity of a 
number of crystalline rocks, and gives the results of a 
series of experiments made in the laboratories of McGill 
University at Montreal. The quantities investigated are 
among the prime desiderata of geological mechanics, being 
involved in the calculation of the velocity of propagation 
of earthquake shocks and in other important questions. 
The only data of this kind previously published seem to be 
open to serious criticism, and the contribution by Profs. 
Adams and Coker is specially opportune and welcome. 
The authors describe the method employed and the pre- 
cautions taken to ensure such accuracy as is possible. The 
rock is cut to the shape of a column 3 inches high and 
1 inch in diameter, either square or circular in cross- 
section. The column is subjected to pressure applied per- 
pendicularly upon its ends, and the resulting longitudinal 
compression and lateral extension are observed. In this 
way are obtained Young’s modulus, E (the longitudinal 
stress divided by the longitudinal compression), and the 
ratio (m) of longitudinal compression to lateral extension 
(t.e. the reciprocal of Poisson’s ratio). The modulus of 
cubical compression (D) is then calculated from the relation 
a mt 
D=1(— JE 
and the modulus of shear (C) from 
C=3( a )E. 
m+ 
From the theoretical point of view these equations do not 
seem to be fairly applicable to the case in hand. A 
crystalline rock is an aggregate of many crystals, each of 
which is anisotropic; and in the case of such a rock as 
granite the crystals belong to a number of distinct 
minerals, differing as regards their elastic constants. The 
argument that an average isotropic effect will result from 
the random orientation of a large number of anisotropic 
crystals is not quite convincing. Nevertheless, the results 
found are reasonable and consistent, and go far towards 
justifying the method adopted. 
When the relation of strain to stress is plotted on a 
diagram, it is seen in every case that the progressive load- 
ing gives a curve not very different from a straight line, 
while the corresponding line for unloading is a curve lying 
very near the other, and returning to the initial point. It 
follows that the rocks examined approximate nearly to 
perfect elasticity, and obey Hooke’s law somewhat closely, 
and with small hysteresis, for pressures ranging up to 
10,000 Ib. or even 15,000 Ib. to the square inch. Many 
of them compare favourably in these respects with cast 
iron. We quote some of the results obtained for the 
seventeen rocks examined. The figures are to be multi- 
plied by 10’ to give the measure in C.G.S. units :— 
D Cc 
Cast iron 6-897 4-132 
Carrara marble 4-090 2-171 
Peterhead granite ... > 3-300 2-340 
Quincy granite... Bat 2-750 1-916 
Nepheline-syenite, Montreal 4-290 2-505 
New Glasgow Anorthosite 5-760 3:275 
Sudbury diabase 7-329 3:700 
It appears that the .granites offer less resistance, both 
to compression and to shearing, than the basic igneous 
rocks. The authors connect the greater compressibility of 
the granites with the presence of quartz, but the granites 
appear to be actually more compressible than that mineral. 
We should suppose rather that the alkali-felspars, which 
constitute the greater part of an ordinary granite, are 
notably more compressible than the ferro-magnesian 
silicates and lime-felspars; and this seems to be confirmed 
by the intermediate value found for the nepheline-syenite.* 
The general character of the rocks which compose the 
bulk of the earth's crust is doubtless fairly represented by 
1 The authors cite Voigt’s value for the compressibility of quartz. The 
more accurate determination by Amagat gives 4212 in terms of the unit 
adopted above. For the felspars there are no known data. 
NO. 1949, VOL. 75 | 
the crystalline igneous rocks selected for investigation, and 
the average compressibility must lie between the highest 
and lowest values tabulated above. A simple average of 
all the igneous rocks examined gives a modulus of com- 
pressibility 4-374 x10'', which is slightly less than that for 
plate glass. In such an average the acid rocks are prob- 
ably over-represented, and the value consequently too low. 
AL H- 
CYANOGENESIS IN . PLANTS AND THE 
CONSTITUTION OF PHASEOLUNATIN. 
G INCE 1900 a considerable number of plants yielding 
= prussic acid have been investigated in the Scientific 
and Technical Department of the Imperial Institute. 
Among these are Lotus arabicus, a plant which grows 
commonly along the valley of the Nile; Sorghum vulgare, 
widely cultivated as a cereal in tropical countries; the 
Lima bean (Phaseolus lunatus) ; common flax; and cassava 
(Manthot utilissima). The source of prussic acid in each 
of these cases has been proved to be a glucoside, which 
in the presence of water is decomposed by an enzyme, also 
occurring in the plant, yielding prussic acid, glucose, and 
a third neutral substance. Three of these glucosides have 
been fully studied by Prof. Dunstan and Dr. Henry. 
Lotusin, C,,H,,0O,,N, from Lotus arabicus, is compara- 
tively complex in structure, and is the lotoflavin ether of 
maltose cyanohydrin, lotoflavin being a yellow colouring 
matter isomeric with fisetin and luteolin, and belonging, 
like these, to the quercetin group of dyes. Dhurrin, 
C,,H,,O,N, from Sorghum vulgare, is a dextrose ether 
of parahydroxybenzaldehyde cyanohydrin. Phaseolunatin, 
C,,H,,O,N, which occurs in the Lima bean, flax, and 
cassava, has been shown to be a dextrose ether of acetone 
eyanohydrin (Phil. Trans., 1901, B, 515; 1902, A, 399; 
Proc. Roy. Soc., 1903, Ixxii., 285; 1906, Ixxviii., 145 and 
152; British Association Reports, 1906, and Ann. Chim. 
Phys., 1907, [viii.], x., 118). 
In a paper communicated to the meeting of the Royal 
Society held on February 28, the same authors, in conjunc- 
tion with Dr. Auld, gave the results of some further investi- 
gations carried out with the object of determining the 
nature of the dextrose residue present in phaseolunatin. 
Fischer and others have shown that glucosides are 
divisible into two classes, derived respectively from the 
a and B forms of the hexoses, and that the glucosidolytic 
enzymes which occur in plants also belong to two groups. 
the one, typically represented by maltase, being capable 
of decomposing a-glucosides, and the other, of which 
emulsin is the best known, having the power of hydrolysing 
B-glucosides. From the results of the examination of the 
sugar initially produced when phaseolunatin is hydrolysed 
by the enzyme, which occurs in association with it in the 
Lima bean, it is clear that this is a-dextrose, and, there- 
fore, that phaseolunatin is the a-dextrose ether of acetone 
cyanohydrin. It is the first naturally occurring glucoside 
of this type so far known. 
This conclusion has rendered necessary a further in- 
vestigation of the enzymes, which occur with phaseo- 
lunatin in the Lima bean, the flax plant, and cassava. 
The mixture of enzymes, prepared in the usual manner 
from the Lima bean, decomposes amygdalin and salicin, 
and may therefore be assumed to contain emulsin. The 
latter, prepared from sweet almonds, has, however, no 
action on phaseolunatin, and this is in harmony with the 
constitution now assigned to the latter glucoside, since the 
emulsin of almonds has been shown to hydrolyse only 
glucosides containing B-sugar residues. 
It has now been found that the Lima bean contains, in 
addition to emulsin, a second enzyme, which is of the 
maltase type, and that the decomposition of phaseolunatin, 
which takes place when the beans are ground up in water, 
is due to the action of the maltasoc-like enzyme. The 
maltase of yeast is also capable of decomposing phaseo- 
lunatin, so that the enzyme which occurs in the Lima 
bean appears to be of the same type as the maltase present 
in yeast. 
The mixtures of enzymes occurring in association with 
phaseolunatin in the flax plant and in cassava have also 
been investigated and found to behave in the same manner 
as the mixture of enzymes prepared from the Lima bean. 
