Adgust 1, 1892.] 



KNOWLEDGE 



1A3 



clond, which formed wlien the oxygen evaporated may have 



beeu due to small particles of solid oxygeu. 



Experiments conducted since those of Cailletet and Pictet, 

 fifteen years ago, have been designed so as to permit of the 

 examination of the physical properties of the liquefied sub- 

 stances. This has been efl'ected by obtaining such low tem- 

 peratures of the material, and such a low temperature of its 

 immediate surroundings, that the evaporation of the liquid 

 (whether hydrogen, oxygen, or nitrogen) only takes place 

 slowly under ordinary atmospheric pressure. In Cailletet's 

 experiments, a liquid was obtained under low pressure, 

 but the surroundings of the liquid were relatively warm, 

 so that the substance could not long remain liquid. In 

 Pictet's experiments the liquid could only be examined by 

 removing it from the cold atmosphere. In the experi- 

 ments conducted by Dr. K. Olszewski, the gas to be 

 experimented on was contained in the innermost of four 

 glass tubes placed one within the other. In the outermost 

 tube was placed solid carbonic acid and ether. By placing 

 this in connection with an air pump, the temperature of 

 the neighbouring tubes was reduced to —100^ C. This was 

 the method for obtaining low temperatures, employed by 

 Faraday in his later researches. Now comes a novelty. 

 Ethylene gas, brought from a Natterer's cylinder, is led 

 into the (second) inner tube. Here it is liquefied by low 

 temperature, and under a considerable pressure. The two 

 innermost tubes (into which the oxygen or hydrogen are 

 presently to be brought) are now surrounded by a tube 

 containing liquid ethylene at about —100^ C. This liquid is 

 protected from the warmth of the air by the outermost 

 jacketing tube of carbonic acid ice. By the action of an 

 air pump the pressure on the liquid ethylene is reduced to 

 10 mm. of mercury (about y^th the ordinary atmospheric 

 pressure) ; dry air at the same time is cautiously blown 

 through the ethylene to prevent its evaporation from 

 becoming violent. The gas (say oxygen) is now passed 

 into the two innermost tubes. The intense cold produced 

 by the evaporation of the liquid etbylene, the liquid being 

 to begin with at about — 100'^ C, liquefies the oxygen, which 

 is under a considerable pressure. But one more device 

 remains to be mentioned, the most singular of all in 

 Dr. Olszewski's process. The tiro innermost tubes, as has 

 been said, contain the liquefied oxygen. They are now both 

 put into connection with the air pump, and the pressm-e 

 is cautiously diminished. The liquid in both tubes begins 

 to evaporate and is thereby chilled. Presently, the liquid 

 in the outer tube begins to evaporate more quickly than 

 that in the innermost one, owing to the fact that it is in 

 contact with the (relatively) warm ethylene tube. The 

 whole of the liquid in the outer tube consequently evapo- 

 rates whilst there still remains a considerable portion of 

 the liquid in the innermost tube. The temperature of the 

 innermost tube has now sunk considerably lower than 

 that of the liijuid ethylene. Nitrogen can be frozen in this 

 way. By diminishing the pressure on the solid nitrogen, 

 and thereby causing evaporation, Olszewski obtained a 

 temperature of —225"" C, or less than 50° C. from the 

 supposed absolute zero of temperature, that is to say, the 

 point at which all the heat has been extracted from a 

 body. 



The exceedingly cold liquid contained in the innermost 

 tube is protected from the relatively warm ethylene by the 

 non-ccndueting layer of rarefied gas in the intermediate 

 tube. Consequently, the substance remains liquid at 

 atmospheric pressure, or even at lower pressure for a 

 space of time (five to fifteen minutes) sufficient to allow of an 

 examination of some of the important physical properties. 

 Thus the specific gravity is determined by measuring the 

 height at which the liquid stands in the tube, hence 



deducing the volume of the liquid ; then collecting the gas 

 after evaporation, and measuring its volume. The weight 

 of a given volume of //'is is, of course, well known. This is 

 necessarily equal to the weight of the liquid before evapo- 

 ration. Hence we know the weight of the liquid in the 

 tube. Its volume having been ascertained in the way 

 described, the specific gravity is readily calculated imder 

 atmospheric pressure ; it is found that — 



Melts at. Boils at. Critical Temp. 



Oxygen ... — -101° - 118-8° C. 



Sp. gr. of litiuid. 

 1-121 at -181-4° C. 

 Nitrogen ... -2U° -191-4° -146° C. 



Sp. gr. of liquid. 



-885 at - 194° C. 

 Hydrogen at — 213°C. lii|uefied under a pressure of 

 190 atmospheres ; with Pictet's temperature of 140° C. a 

 pressure of 650 atmospheres was required. The tempera- 

 tures recorded in the above observations were aU registered 

 with a hydrogen thermometer. The critical point of 

 hydrogen is — 220' C. 



BEE PARASITES.-II. 



By E. A. Butler. 

 (Continued from pa^/e 128.) 



THE economy of the solitary bees is, of course, quite 

 unlike that of the social species, and it will be 

 anticipated that the parasitism from which they 

 sufl'er is also of a dift'erent type. In solitary bees 

 the species consist only of males and females, and 

 hence all the labour necessary for the rearing of the young 

 falls upon the latter sex. They excavate tunnels in sandy 

 or clayey banks, posts, trees, or wherever else the habits of 

 the particular species dictate, and in these burrows cells 

 are arranged, each intended for a single grub ; the eggs are 

 deposited upon a previously provided stock of food, con- 

 sisting chiedy of the pollen of fiowers, often made up with 

 a little honey into small pellets. As the larva, like that of 

 the hive bee, is a footless maggot, quite unable to leave 

 the cell in which it is cradled, and is not continuously 

 tended by its parent, the amount of food provided must be 

 such as wiU last it during the whole of its larval life. This 

 quantity is not large, considerably less in fact than might 

 have been expected, but its amoimt has, in some inscrutable 

 way, to be correctly estimated by the mother bee. A slight 

 deficiency in the amount would probably not be fatal to 

 the life of the grub, but would rather result in dwarfing 

 the size of the insect produced ; hence the physique of the 

 race would seem to depend in great measure upon the 

 accuracy of the mother's estimate of the amount of food 

 her offspring will require. 



When the pea-like globtde of bee food has been provided, 

 the egg laid, and the cell closed, the mother's work, so far 

 as concerns that particular member of her family, is done ; 

 her other toils consist simply of repetitions of these opera- 

 tions on behalf of the remainder of the brood. Many 

 journeys abroad and much diligent work therefore devolve 

 upon her before she has fully discharged the function she 

 has to perform in the world ; and as the collection of 

 pollen and the construction of the burrow and its cells are 

 dependent to a great extent upon weather, since bees have 

 a great dislike to cold and windy or damp days, the com- 

 pletion of the important task of laying the foundation for 

 next year's race will often, in the uncertamties of our 

 English climate, become a rather protracted business. As 

 so much outdoor work is involved, it is clear that the 

 burrows will often be left by the solitary owner unprotected. 



