THE AUSTRALASIAN JOURNAL OF PHARMACY. 
325 
Dilatancy. 
Prof. Osborne Reynolds, of the Owens College, Manchester, has discovered 
a new property of matter, to which he has applied the term Dilatancy . It is a 
property of granular matter probably connected with gravitation. If one were 
asked what would happen in case a caoutchouc bag filled with sand and water, 
and joined by a tube to a reservoir of water, were to be squeezed, the answer 
would most likely be that the sand and water, or the water only, would be 
pressed out of the bag ; but Prof. Reynolds found the opposite to take place. 
The more the bag was squeezed the larger it became. 
“ As the result of a long- continued effort to conceive a mechanical system 
possessing the properties assigned by Maxwell, and, further, which would 
account for the cohesion of the molecules of matter, it became apparent that 
the simplest conceivable medium— a mass of rigid granules in contact with 
each other— would answer, not one, but all the known requirements, provided 
the shape and mutual fit of the grains were such that, while the grains 
rigidly preserved their shape, the medium should possess the apparently para- 
doxical or anti-sponge property of swelling in bulk as the shape was altered.” 
If the grains interlock, any alteration of form or relation must, under given 
conditions, increase the space occupied. The size of the grains is not important 
as long as either of two conditions are satisfied — firstly, that the medium is 
continuous, infinite in extent ; or, secondly, that the grains at the boundary should 
be so held as to prevent a re-arrangement beginning. Prof. Reynolds used a 
thin indiarubber bag having a capacity of six pints. The bag being filled with 
clean, dry sand, was joined to one leg of a mercury pressure-gauge ; when the 
bag was flattened between a couple of boards the mercury rose seven inches in 
the leg next to the bag ; therefore, a partial vacuum was formed by squeezing 
the bag. Suppose that water be used, the sand being at its closest order, and 
the mouth of the bag be closed so that it cannot draw any more water ; when 
pressure is applied that bag does not alter in shape ; it could not do so without 
enlarging its interstices ; these cannot enlarge without drawing more water, and 
this has been prevented. On opening the neck to allow the entrance of water 
the bag at once yields to a slight pressure, and changes its shape ; but if the 
mouth be closed again no further change in the shape of the bag can be effected. 
A familiar instance of this property is seen when walking along a wet 
beach; around each foot-print the sand is seen to change colour for some dis- 
tance. This is because the pressure of the foot has changed the shape of the 
mass under it, and the water is sucked in (instead of being squeezed out), drying 
the sand all around. 
The Phaemacognosy of the Niteites. 
Under the above title Mr. G. A. Atkinson, M.B., has published a paper 
in the Pharmaceutical Journal wherein he shows that the crystallised nitrite 
of sodium is the best inorganic salt for use in medicine. Its solubility in 
distilled water is 1 in 1'14 ; and a solution, in the absence of ferments, and of 
stronger acids than nitrous, is perfectly stable, but is apt to be the seat of a 
form of mould if exposed to the air, and such growth naturally causes deterioration 
in the strength of the solution. It may be used for administration by the 
stomach, a little sodium bicarbonate preventing its decomposition by the gastric 
juice. It is also the best nitrite for hypodermic injection. This experimenter 
considers the nitrite of amyl to be the best organic nitrite, being more stable 
than ethyl nitrite, and the most suitable for inhalation. 
Nitro-glycerine or propenyl tri-nitrate (C 3 H 5 N0 3 ) is practically unacted on 
by the gastric juice, a point of importance where absorption without decom- 
position is desired. A soluttion of 1 in 1000 of distilled water — dose 5 to 30 
minims — is recommended for administration by the stomach. 
