WITHDRAWN FROM THE ACTION OF GRAVITY. 435 



season has intervened, diminishing the persistence of the bubbles, and I have 

 been forced to postpone my attempts till a more favorable period. 



Note on the preparation of Oie glyceric liquid with tJie impure glycerines of 



commerce. 



The first glycerine which I ti'ied was that sold by the apothecaries of Ghent. 

 It is of an intense yellow color and disagreeable odor, and contains in large 

 quantity a foreign substance, which I believe to be lime, and of which it is ne- 

 cessary to rid it. After many fruitless attempts, the following process occurred 

 to me, and has been attended with considerable success : Mix in a flask a suifc- 

 able quantity of distilled water and an equal quantity of the glycerine in ques- 

 tion ; then introduce into the flask a quantity of Marseilles soap cut in thin 

 shavings, whose weight should be about a fifteenth of that of the water ; these 

 shavings remain floating on the liquid. The soap should have been kept in a 

 moist place ; if dry, the action is scarcely appreciable. After five minutes the 

 flask is to be slowly turned three or four times, when small white particles will 

 be seen to be detached from the soap and disseminated through the liquid, and 

 which, when the flask is left at rest, gradually ascend. The slow turning is to 

 be repeated at intervals of five minutes, for an hour and a half; the particles 

 become more and more numerous, and eventually and permanently fill the whole 

 mass. The greater part of the soap remains unattacked, but an excess was 

 needed in order to present the more surface to the action of the liquid. This is 

 disengaged from the particles and the excess of soap by passing it through a 

 filter formed of cotton stuff of close texture ; when a new supply of the soap- 

 shavings equal to the first is introduced, and the turnings are to be repeated as 

 before for the space of an hour, the particles again form and must be separated 

 anew by filtering ; the liqupr now passes in a milky state, but is rendered lim- 

 pid, or nearly so, by filtering it through paper ; the preparation is then com- 

 plete. All these operations should be conducted at a time when the outer tena- 

 perature and that of the apartment are from 18° to 20° ; if this last limit be 

 greatly exceeded the liquid will dissolve too much soap. A bubble formed of 

 this liquid and deposited on a ring, as indicated in §§ 13 and 15, may subsist 

 for perhaps an hour and a half. This liquid, however, has one serious incon- 

 venience ; at a temperature below 18° it tails altogether to yield bubbles; hence, 

 when Ave wish to use it in winter, it is necessary previously to keep the flask 

 for about an hour in water maintained at 20°. It is needless to add that tlie 

 apartment should be warmed. 



I have tried, in the second place, a glycerine which came, as I was assured, 

 from Paris. It has the same color and the same odor with that from Ghent 

 When mixed with the solution of soap the compound is at first slightly turbid, 

 and after some houi'S becomes very milky. If this liquid be left at rest the 

 precipitate, as in the case of the glycerine of London, already described, ascends 

 gradually, and forms in a few days a distinct layer on the top. Here, also, the 

 limpid liquid should be withdravvTi by means of a siphon. The proportions 

 which I have used with most success are five volumes of glycerine and four of 

 the same solution of soap employed for the glycerine of London. The liquid 

 thus obtained yielded bubbles which lasted five quarters of an hour. This trial 

 was made in autumn, at a time when the external tcmpei-ature did not rise above 

 7° or 8*^, by operating in a warmed apartment, but without any other precau- 

 tion. It is probable that the same liquid prepared in summer would furnish 

 films of a still greater persistence. 



I am led to believe, from what I know of the different processes by which the 

 glycerines of commerce are obtained, that all that can be procured are analogous 

 to one or other of the three which I have employed ; hence it will be seen that 

 the best course is to obtain the substance from London, provided none as pure 

 can be found elsewhere. 



