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wer end of. the: Se feabes “The ‘upper el oh ‘the: steam-jacket tapers likewise 
al is ‘closed bya cork carrying the thermometer. Directly above the partition, a 
prken is connected in order to conduct the condensed liquid back into the boiling 
tube. The syphon is bent down slightly, before entering the lower part of the steam- 
jacket, ‘so that a- small amount of liquid may accumulate therein and: thus block up 
the connection for ascending vapours. At the opposite side of the steam-jacket the 
“outlet pipe. branches off which first is bent upwards and is connected with the efflux j 
¢ ondenser by a cork or by grinding-in. The jacket of the condenser measures about 
10 ‘cm. The boiling vessel stands in the centre hole of an asbestos plate with a 
diameter ‘of 2.cm., “and. closed beneath with brass wire gauze. The asbestos plate 
n must be sufficient in size (diameter about 10 cm.) so as to keep off the radiant heat 
of the burner from the thermometer. It is advisable, especially with liquids boiling 
: above 100°, to surround the boiling tube with an air- jacket of 5 cm. diameter and 
; 22cm. height. The thermometer must be inserted sufficiently deep into the steam tube 
so that the mercury thread is to its whole extent. surrounded with living steam. The 
eight of the flame must be regulated so that the liquid just comes to vivid boiling. 
z We beg to add two remarks in addition to-the preceding abstract. | 
K. The one of them comprises the suggestion to make use of certain standard pressures” : 
= en quoting boiling points, more especially vacuum boiling points. At present, every 
a uthor quotes the pressure as recorded directly by his apparatuses, and leaves it to 
“his fellow-chemists how to make use of his statements. Recalculation for the differing — 
. purposes of other authors must, therefore, be repeated so often as use is made of the 
‘statement. ‘concerned. It goes without question that scientific technique would derive 
a a great benefit from. the adoption of a certain standard user: to which the vacuum 
; readings should in future be adjusted. — | 
For ordinary distillations, a normal pressure is given by the “mean” ’ barometric 
pbeight of 760 mm. mercury column. For vacuum boiling points, C. von Rechenberg 
(Theorie der Gewinnung und Trennung der iitherischen Ole, Leipzig 1910) made use of 
“certain pressures: 10, 20, 50, and 100 mm. mercury. All these quantities are, however, 
i 1no connection with the scientific system of measurement. Hence, it seemed advisable 
= 
ce of one dyne on one square centimeter. One atmosphere equals 1013200 “bars”. 
0 the multiples of this unit lying in the neighbourhood of the usual vacuum pressures, 
10000 “bars” (= 10 “kilobars”) corresponds nearly to 7,5 mm., and 20 “kilobars” to 
15,0 mm. mercury; both pressures are, therefore, serviceable as standard pressures 
é % may be supplemented by the multiples 100 “kilobars” = 75,0 mm. and 1000 “kilo- 
s” = 750 mm. In this way, the “atmosphere” would come in connection with the - 
ae system of measurement, a fact to which already Ostwald!) has drawn attention. . 
% As was remarked above, this suggestion as to normal pressures dlone is not ~ 
suf ficient. If it really shall be a question of saving accessory work, the statements _ 
cor icerning boiling points in the literature. must be recalculated, at least as far ass 
they are quoted by the text-books. On the. other hand, fellow-scientists should 
en deavour to recalculate their new readings taken at optional pressures to one of the 
normal pressures, or still better make use directly of a normal pressure. The contri- 
vances required therefor are universally known; in the simplest form they consist of 
Lt rottle cock in connection with a second cock for exact regulation, about in the 
manner of a 3. Spo 7% Z : 
Fs 
F) 
| 
Bs Grisnitrise ae allgemeinen Chemie, Leipzig 1899, p. 54. 
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resort: to the absolute unit of pressure, termed one “bar? and defined as the | 
