326 Robiiiet on Pur^ying Crystals. 



that the mortar should be kept for ten or twelve hours before it 

 is used, in order to acquire a certain degree of consistence ; and 

 that it may be perfectly relied on, if, by a preliminary trial, it is 

 found to harden in three or four days ; his experience having 

 invariably shewn that the mortars which harden soonest, are also 

 the most tenacious. — AnnaUs de Chimie et de Physique, Mars 

 1826. 



9. On a New Method of Purifying Crystals ; by M. Ro- 



BINET. 



Every practical chemist knows how difficult it often is, parti- 

 cularly in the analysis of organic substances, to clear away from 

 crystalline products the mother water, and other heterogeneous 

 matters, which collect in their interstices. When the crystals 

 are very fine, and still more when they are soluble in the ordi- 

 nary menstruums, it is sometimes impossible to clear them, al- 

 though perfectly pure, by any other method than repeated 

 crystallization and digestion with animal charcoal ; both of 

 which processes are troublesome, and occasion considerable loss. 

 M. Robinet has proposed a new and very simple method, which 

 was suggested to him, in consequence of observing that, when a 

 parcel of crystals came into contact with the mouth of the pi- 

 pette during the act of suction, they were instantly and perfectly 

 cleaned. The process depends on the transmission of a current 

 of air through the crystals. He has suggested various forms of 

 apparatus for the purpose. The simplest consists of a double- 

 mouthed bottle, with a funnel in one mouth, and a bent tube in 

 the other ; the lower opening of the funnel being obstructed by 

 a ball of cotton-wool, and the crystals placed above the cotton. 

 On sucking the air through the crystals by a bent tube, they are 

 . cleaned in a few seconds ; and, if necessary, the operation may 

 be repeated after previously introducing a little water into the 

 funnel. A convenient way of constructing the apparatus so as 

 to work of itself, is to make the second tube reach the bottom 

 of the bottle with one limb, and with the other a vessel of wa- 

 ter situated on a lower level. The whole bottle and tube being 

 filled with water, the funnel is to be introduced, and the water 

 then allowed to run off by the syphon. On the large scale a 

 more suitable apparatus will be a tube from a steam-boiler, by 

 which the bottle may be filled with st^am from time to time, 



