418 Progress in Science. {July, 
entirely from those on the tube fronciple almost universally employed. 
The substance to be cut is attached to a plate worked by a screw somewhat 
after the manner of the well-known slide-rest of the lathe; the contrivance 
which is adapted for cutting sections of either hard or soft substances, has 
means of keeping the saw or knife rigidly in position while at work. Among 
the substances used for imbedding tissues to be cut, carrot and elder-pith 
seemed to offer especial advantages. The process of freezing soft tissues 
gives good results, and is convenient, because the tedious process of hardening 
with alcohol or chromic acid is dispensed with; gum-water should be used 
for imbedding, as water when frozen blunts the knife at the first cut, owing to 
its becoming crystallised. 
Heat.—M. Berthelot, writing on refrigerating mixtures, says the thermal 
effe& produced when ice is mixed with bihydrated crystallised sulphuric acid 
is the sum of three effects, viz., the fusion of the acid and that of the ice, 
which absorb heat, and the combination of the two liquids, which liberates 
heat. The numbers obtained in practice are under those calculated from 
theory, owing to loss through radiation. The author shows from theory that 
no method of cooling is comparable to vaporisation, and he thinks that much 
higher temperatures may yet be had by means of it. 
In prosecuting experiments to ascertain the expansion of various 
substances by heat, the following experiment was tried:—The bulb of 
a thermometer was suddenly plunged into melted lead. The mercury 
instantly darted down far below zero. The action was so quick that the 
point could not be ascertained. This was caused by the sudden expansion 
of the bulb by heat before it reached the mercury by conduétion; this 
then began to rise very rapidly, and before it had arrived at the top of 
the tube the bulb was withdrawn. The experiment requires adroitness, 
for, as we all know, the instant that the mercury touches the top, the 
bulb will burst. This must be greased before immersion in the fused lead, 
otherwise a film of the metal will adhere and retain sufficient heat to carry 
the mercury to the top with a consequent fracture. A thermometer treated 
in this rough manner afterwards showed an index error of six degrees, the 
mercury having risen to that extent ; but after a few days the equilibrium was 
partly restored, and the error remained permanently at three degrees. 
Dr. H. Beins in considering the question how to transform heat into 
mechanical power more advantageously than it is done in our common steam 
and other engines, found that when natrium-bicarbonate (or the corresponding 
salt of kalium) in a dry pulverised state or in a watery solution is heated ina 
closed space, a part of the carbonic acid is given off and condensed in a not 
heated portion of that space, so that at a temperature of 300° to 400° C, 
liquid carbonic acid can be distilled out of those salts with a tension of from 50 to 
60 atmospheres. The author hasexperimentally found that a carboleum-engine 
is easily constructed. Taps and joints can be made to answer perfe@ly. A year 
ago he filled a tube of hammered copper with carbonic acid of 50 atm., and 
not the least loss is as yet observed. Wrought metals are therefore not 
permeable for gases of that tension. Perhaps the phenomena of porosity, 
belonging to the common air-pump experiments, are partly caused by surface- 
condensation. For the great industry, the carboleum-engine can in almost 
every case substitute the steam-engine. For the small industry, specially 
for engines working with intermissions and during brief spaces of time, the 
property of carboleum of being always ready for work is of much importance; 
for instance, for printing-presses, fire-engines, street-locomotives, &c. By this 
same property, and since the mechanical equivalent of electricity is very small, 
a carboleum-engine is a fit and cheap source of electrical light. This method 
of compression furnishes easily the required tension for the conveyance of 
letters in tubes, and the modern break apparatus for railways. Perhaps the 
property of carboleum of possessing a power of projection a hundred times 
cheaper than gunpowder can be made use of. The fact that a carboleum- 
engine with sufficient store of carboleum is independent of our atmosphere, 
makes it possible to construct a vessel, provided with means to sink to any 
depth of the sea, to rise and sink at will, to cruise about under water, and to 
maintain the life of the crew during that operation, to develop light, &c. The 
