!26 



NA TURE 



[Feb. 3, 1887 



present some points which I do not think have been 

 generally observed. 



Aquatic plants at the bottoms of ponds give ofif oxygen 

 gas, and marsh gas is emitted from decaying vegetable 

 matter. These two sources of supply will, to some 

 e.xtent, account for the entanglement of bubbles in ice on 

 a pond surface, but only to a very small extent, and may 

 be left out of consideration in dealing with the develop- 

 ment of air-bubbles in ice. This takes place independ- 

 ently of any extraneous source of supply other than 

 atmospheric air, and may be as well seen in a glass or 

 earthenware vessel as over a weedy pond surface. 



The following facts must be noticed : — 



(i) Ice over deep water invariably contains fewer 

 bubbles of included air and gas than ice formed over 

 shallow water, and probably from this cause ice obtained 

 from over deep water is more durable for storage than ice 

 obtained from shallow pools. 



(2) The upper or surface portion of a coating of ice 

 invariably contains less included air than its under or 

 lower portion, and this is more obvious in ice formed over 

 shallow than in that over deep water. In each case there 

 is a fairly regular gradation in the quantity of entangled 

 air, increasing from the surface downwards. I ascertained 

 that the included air from the upper surface {a, Fig. i) of 



Ficj. 1. 



Iicj.2. 



^ 



a thin coat of ice was scarcely appreciable in quantity, and 

 one pound weight from its lower surface [b, Fig. i) con- 

 tained o'oS of a cubic inch of entangled air. 



(3) There is more included air in ice formed over water 

 in a small vessel (Fig. i) than in ice formed over a large 

 body of water. 



(4) There is more included air (weight for weight of 

 ice) in an entirely frozen mass of ice (Fig. 2, d) than in 

 surface ice from a partly frozen vessel of water. In an 

 entirely frozen mass (Fig. 2, (/) i pound of ice contained 

 o'59 cubic inch of included air ; and surface-ice (a, b. 

 Fig. i), over unfrozen water, one pound weight contained 

 o'i5 cubic inch. 



(5) In freezing separately the water from which the first 

 frozen coat of ice had been removed (Fig. i, c), the ice 

 contained a much larger proportion of included air (o'Sg 

 cubic inch) than either the surface ice (Fig. i, a, b) or 

 the ice obtained from entirely freezing a body of water 

 (Fig. 2, d). 



(6) On re-freezing water which had been frozen and 

 thawed, there was but a very slight further release of air, 

 which had been almost entirely released in the first 



freezing : one pound of the second ice contained but 0^005 

 cubic inch of air. 



(7) In completely freezing a vessel of water(Fig. 2), not 

 only does the entangled air increase in quantity down- 

 wards, but at the base of the frozen mass occurs a large 

 air-cavity (f. Fig. 2). 



All these facts, and the results of the experiments, seem 

 to point to the fact that, in the process of freezing, the 

 elimination of the air and gases in solution is taking 

 place in two directions: (l) a part of the air is taken 

 into solution by the ?<«frozen water as it is progressively 

 rejected by the thickening coat of ice ; and (2), a 

 part of it is extruded as bubbles of air, which become 

 entangled in the ice. 



If each stratum of ice eliminated the whole of its own 

 proportion of air in solution in the gaseous form, the 

 bubbles would be distributed with fair regularity through- 

 out the collective mass, but their progressive increase in 

 a descending direction exactly agrees with the continuous 

 surcharging of the underlying unfrozen water with the 

 air in solution rejected by the ice above, till, at the end 

 of the freezing process of the mass, the remnant is ex- 

 truded as one large bubble (Fig. 2, e) at its base. 



The rejection of the air into continued solution would 

 seem to take precedence of its extrusion in the gaseous 

 form, and would go on as long as there was a sufficient 

 body of adjacent water in a condition to receive it ; but 

 the gradual surcharging of a limited body of water with 

 the rejected air is necessarily accompanied by its pro- 

 gressively increased extrusion in the gaseous form. 



The comparative absence of air-bubbles in ice over 

 deep water is accounted for by the fact of there being a 

 sufficient body of adjacent water in a condition to receive 

 the rejected air into solution in preference to its extrusion 

 as gas. 



To briefly recapitulate the experimental results: — (i) 

 In a thin ice-coating, the upper or surface half contains 

 barely a trace of eliminated air, whilst its under or bottom 

 half contained 008 cubic inch of air in each pound of 

 ice. (2) A surface coating of ice i^ inch thick contained 

 o'i5 cubic inch of air in each pound weight, whilst an 

 entirely frozen mass contained o'59 cubic inch of air 

 in each pound weight. (3) The freezing of a limited 

 body of water which had been first frozen over and the 

 surface ice removed points still more strikingly to the con- 

 centration of air in solution ; for this contained o'Sg cubic 

 inch of air in each pound weight, compared with o'i5 

 cubic inch in surface ice, and o"59 cubic inch in an 

 entirely frozen mass. 



The water employed in these experiments was from the 

 East Surrey Waterworks. GEORGE M.wv 



NOTES 



The fallowing notice of motion has been given by Mr. 

 Howell, M.P. : — "To call the attention of the House to the 

 subject of technical education, and to move the following reso- 

 lution : — ' That, in the opinion of this House, it is essential to 

 the maintenance and development of our manufacturing and 

 agricultural industries, in view of the rapidly increasing compe- 

 tition of other nations, both in home markets and abroad ; and 

 in consequence of the almost universal abandonment of the 

 system of apprenticeship ; that our national scheme of education 

 should be so widened as to bring technical instruction, the 

 teaching of the natural sciences, and manual tiaining, within 

 the reach of the working classes throughout the country.' " 



It is staled that in consequence of the financial difficulties of 

 the Bristol College, and lack of endowments, the salaries of all 

 the Professors will be reduced by the Council, and some Chairs are 

 to be abolished. The course pursued by the Council has given 

 rise to much correspondence in the local papers during the past 

 month. It is earnestly to be hoped that circumstances may yet 



