294 



on a little clay-stove, and heat by means of a veiy small gas-flame 

 or of a spirit-lamp to 120°, and keep at tliis temperature for about 

 an hour. After a few trials the operator will soon become accus- 

 tomed to control the tempei-ature at nearly 120°, by placing the 

 flame at the requisite distance from the air-bath; and by using for 

 drying operations of this kind the same stove, the same lamp, and 

 the same length of flame, no new trials for regulating the degree of 

 heat will be required afterwards. A diff'erence of a few degrees 

 above or below 120° is of no consequence; but the merciuy should 

 never fall below 115° nor rise above 125°. After the substance 

 has been thus heated for an hour, remove the flame, cover the 

 crucible with the lid, shut the air-bath, take out the crucible when 

 quite cold, place on a balance and determine the loss of weight. 



Afterwards the same process of heating and weighing is once 

 more to be repeated ; if the second result agrees exactly with the 

 fii-st, or if it only difiers by a few milligi-ammes, no third trial is 

 required ; else the heating process has to be I'epeated a thh'd time 

 or more, until with two following operations the same result be 

 obtained. 



Lastly the loss of weight is calculated for 100 parts, and the 

 result is registered as the amount of percentage of water of the 

 substance. 



II. — Treatment with Ether, 



Place 10 gi'ammes (or less, see above) of the air-dried and 

 possibly fine reduced substance into a glass flask of ^ to § litres 

 capacity; add of ether of 0*720 until after thoroughly soaking the 

 substance is covered ^ or 1 inch high by the liquid, secure the 

 flask with a cork and shake occasionally, taking care lest portions 

 of the contents should get into the neck of the vessel. Having 

 left it to macerate for four days, lift the cork a little, warm the 

 flask in a water-bath or in any other manner to a tempei'ature 

 below the boiling-heat of ether (36°) for a few hours, remove the- 

 mattrass, and again macerate for two days. 



Now transfer the contents of the flask (should the ether contain 

 a great quantity of oil, resin, &c., pour out first the liquid so far as 

 it easily can be removed, and after it has passed the filter, add the 

 remaining substance with the aid of small quantities of fresh 

 ether), into a displacement appai-atus, rinse the flask rej^eatedly 

 with ether, and wash the substance with this and with small 

 quantities of ether until the latter assumes not only no colour, but 

 leaves, on evaporating a few drops on a watch-glass, no residue of 

 any consequence. 



To push the washing to this degree, requires mostly much ether 

 and also time, but it is necessary in order to prevent (1) that 

 any portions of the constituents, soluble in ether, should be lost ; 



