40 Prof. J. Plateau on the Figures of Equilibrium 



in my Fifth Series, the best. Other kinds of glycerine, how- 

 ever, which are much less expensive, are now manufactured in 

 Prance by the same processes, and might perhaps be used if 

 needful in place of Price's glycerine; but it would be necessary 

 to employ them in different proportions. I have always got the 

 best results in summer ; I shall therefore confine myself here to 

 describing the new process as I practise it at that season. 



It is desirable to choose a period of warm weather, in order 

 that the temperature of the room, at least during the day-time, 

 may not fall below 20° C. during any part of the whole process. 

 Marseilles soap which has been recently bought, and therefore 

 still contains its full quantity of moisture, is the best ; this is to 

 be cut up into very small pieces and dissolved at a moderate 

 heat in forty times its weight of water. When the solution has 

 returned nearly to the temperature of the room, it must be fil- 

 tered, and 3 measures of this solution and 2*2 measures of 

 Price's glycerine are to be poured into a bottle ; the bottle must 

 be well shaken, long enough to ensure a thorough mixture of 

 the liquids, and then left to itself for seven days. On the 

 morning of the eighth day, the bottle is to be put into water 

 cooled by stirring pieces of ice in it, so as to lower its tempe- 

 rature to about 3° C, and this temperature must be kept con- 

 stant for six hours by adding fresh ice as it may be required. 

 The liquid next requires to be filtered through very permeable 

 paper; but the liquid in the filter must be prevented from getting 

 warm again, otherwise the precipitate which has been caused by 

 the cooling might partially redissolve. For this purpose, before 

 pouring any of it on the filter, a small wide-mouthed stoppered 

 bottle of an elongated shape is filled with bits of ice, the stopper 

 put in in order to make it heavier, and laid in the filter so that 

 one side of it rests upon the filter ; the bottom of the bottle in 

 which the funnel is supported should likewise be surrounded 

 with ice. The solution is now to be taken out of its cold bath 

 and immediately poured upon the filter; the first portions 

 which pass are turbid ; but it rs only necessary to pour them 

 back into the filter two or three times in order that the liquid 

 subsequently collected may be perfectly limpid. There is no 

 need for me to add that, if the filtration lasts rather long, the 

 ice in the small bottle must be renewed every now and then. 

 The ice placed round the lower part of the bottle in which the 

 filtrate is collected is simply for the purpose of preventing the 

 turbid portions which pass through at first from getting warm. 

 If there is a large quantity of the liquid, it is necessary to dis- 

 tribute it upon several separate filters all acting at once. After 

 filtering, the liquid must be allowed to stand for ten days ; and 

 the preparation is then complete. 



