ELEMENTS OF MATERIA MEDICA.
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3. By heating binoxide of manganese with about its own weight ofstrong sulphuric acid in a glass retort. —The quantity of acid to beemployed should be sufficient to form with the binoxide a mixture havingthe consistence of cream. This method is followed only when an ironbottle cannot be procured, or when a small quantity of gas is wanted ata very short notice. One equivalent, or 44 parts, of the binoxide, yieldone equivalent or 8 parts of oxygen, and one equivalent or 3(1 parts of theprotoxide of manganese: the latter substance forms, with an equivalentor 40 parts of anhydrous sulphuric acid, one equivalent or 76 parts of sul-phate of the protoxide of manganese.
SUBSTANCES USED.
44 ^ j ec t ()x >’K en 8 _ ..1 e q
40
eq. Protox. Mang. 36-
1 eq.Hydr.
I
Oxygen 8leq. Sulph". Protox. Mang. 76
Properties.— It is el astic, colourless, odourless, tasteless, incombustible,but a supporter of combustion. According to Dr. Thomson, 100 cubicinches of this gas weigh, at the temperature of 60" Fah., and when thebarometer stands at 30 inches, 34 60 grains: hence itsspecific gravity is Pill. According to Berzelius and
Dulong, the spec. grav. is PI026. Its atomic weight
is 8: its atomic volume 0 - 5, hydrogen being in both
cases unity.
Characteristics. —If a taper or match be plunged into this gas afterthe ilame has been blown out, but while the wick or charcoal is yet glowing,the flame is instantly reproduced. The only gas likely to be confoundedwith oxygen in this respect is the protoxide of nitrogen, from whichoxygen is distinguished by exploding it with hydrogen. A mixture ofone volume oxygen and two volumes hydrogen, yields, by explosion,water only, whereas a mixture of one volume of the protoxide of nitrogenwith one volume hydrogen, yields water and one volume of nitrogen.
Physiological effects. — (a.) On vegetables. —Oxygen gas is essential j
to the germination of seeds, and to the existence and growth of plants.In the shade vegetables absorb it from the atmosphere, and evolve anequal volume of carbonic acid; while in the solar rays the reverse changestake place; carbonic acid being absorbed and oxygen expired. Thevigorous growth of plants in inclosed cases, as originally proposed andpractised by my friend Mr N. B. Ward ( Companion to the BotanicalMagazine for May, 1836), does not invalidate the above statements;since the cases are never completely air-tight, but allow the ingress andegress of air consequent on changes of temperature.
The effects of pure oxygen gas on germination and vegetation havebeen examined by Theod. de Saussure (Recherches Chimiques sur laVegetation, 1804). He found that the period of germination is the samein oxygen gas as in atmospheric air, but that seeds evolve more carbonicacid in the former than in the latter (pp. 11 and 12). Plants do notthrive so well in an atmosphere of oxygen gas in the shade as in one ofcommon air; they give out more carbonic acid, which is always injuriousto vegetation in the shade. When exposed in oxygen gas to the directrays of the sun, they augment in weight about as much as in atmosphericair (p. !)3, op. cit).