971
NEW INSTRUMENT FOR REDUCING GAS VOLUMES.
The heat of solution is independent of the concentration when this is less than about 0.3 molal. 6. Pure P-anhydrous milk-sugar has been prepared by a n improved method of slow crystallization, and a delicate test shows that it is free from hydrate. Its specific gravity a t 20’ is 1.59,that of the hydrate being 1-54. 7 . The present data on the heats of solution confirm quantitatively
the view that the crystalline substance which alcohol and ether precipitate from cold stable milk-sugar solutions is not a pure substance a s was first supposed but is a mechanical mixture of the hydrate and the P-anhydride. It does not show mutarotation when redissolved in water because the two substances are present in it in the same proportions approximately in which they occur in stable solutions. 8. When the temperature of a stable solution of milk-sugar is suddenly changed a slight thermal lag is observed in its rotatory power, which indicates that the hydration is slightly increased with rise of temperature between o o and 100’. The direction and magnitude of this lag agree with the conclusions drawn from the observed value of the heat of passage. 9. The final heat of solution of hydrated milk-sugar is calculated from the solubilities a t I j O and 2 j t o be -I 1 . 5 , agreeing with the calorimetric measurement a t 20°, which gives -11.4. U N I V E R S I T YOF I L L I N O I S ,
L-RBANA. ILL.
A NEW INSTRUMENT FOR REDUCING GAS VOLUMES TO STANDARD CONDITIONS. GRANTT. DAVIS. Received April I , 1908. BY
The necessity for making a considerable number of accurate measurements of gas volumes has led t o the working out of the following device ior their reduction to standard volume. Since all that is necessaryfor the physical reduction of a gas t o standard volume, is to subject it to a definite pressure, a water column of variable length was first tried, but this was discarded in favor of a column of known length with a fixed scale. The length of the column of mercury (L,) necessary to compress a, gas to standard volume a t temperature “ t ” is found by the formula, V = v(P -P’) 760(1 at)’ the conditions being such that v = V ;then p = 760 (I +at) p’ and I,, = fi - 760. The length for the water column was taken as I, x 13.59,and correction was made for the expansion of water with rise in temperature. The apparatus for use with gases which can be collected over water consists of a piece of iron pipe about two meters long, fitted with a T near the top and a n elbow a t the lower end. The elbow is closed by a rubber
+
+
972
GR.IST
T.
DAVIS.
stopper carr!-ing a glass T, one arm of which is fitted with a stopcock, and the other connected t o thc water .;~ippI!-. Thc T a t the upper end of the pipe carries a siiilill re.crvoir a t I lict top to prevent o\-erliow in case of too hasty filling, and Ihe ~;.de-openiiigis closed b y a rubhcr stopper carrying :i siphon with ;t T.er?- short inner legq and t h e long 1c.g emptying into the sink, or a s ~!ion-iiin th:: fig-un. 1 o the lower part of i i 1 C pilw is :ittached a scale. so graduatcd in timi the column of water from the hotton1 of tlic liort leg of the siphon t o ilie ;y‘icluriqLio:! is t h v calculnted lerigtli for t l i c ;cnipcmiurc rcprcsciitcd 1:). t h e graduation. .litachcd t o this “t~~iiiperntiire” scale, is G sliding “ p r c s s u x ” sale ~rliosedix-isions ;ire I ,? 0 111111 long. ’i‘o aI.oic1 the error which \rould be introduced !)y using tap waicr of a temperature diflerciit from that of tlic room, the s!-stern 01’ 1)ottlcs ‘*-I” ‘,I3 is introduced. “-1” coiitaitis distilled \rater a t the room temperature. ’!‘ap water being admitted t o ” : 3 . ” the water from ‘.-I” is forced into the aplxratus. and no temperature change 0 ccu rs . ’1‘0 use the apparatus the burette containing the gas is connected t o the T a t the bottom of the pipe and the stopcock opened. Care must be taken t h a t there is no air in ‘Lsink t h e connecting tube. The graduation 760 on t h e pressure scale is placed opposite that point on the temperature scale which corresponds t o the observed temperature, water is admitted t o the pipe until the siphon begins t o a c t , a n d while a slow stream continues t o flow, the meniscus in the burette is brought level with that graduation of the pressure scale which corresponds t o the observed barometric pressure, and the corrected volume of the gas read off. The position represented in the figure is that for a gas ohserwd at. a temperature of Z I . ~ ’ ,and barometric pressurc of 754 mm. gives the length of water column necessary t o compress a Table gas t o the standard volume for temperatures from 1 5 O t o 34O. Table “ B ’ ’ offers a comparison between the standard volume as calculated, and as observed by means of this instrument. ? .
A LECTURE TABLE DOWN-DFL4FT.
973
TABLE“A.” cm.
T. 15
73.9
16
79.2
25 26
I7
84.0 89.2
28
I8 I9
126.9 132.7 138 7 144.4
27
94.2
29 30
IjO.j Ijj.O
31 32 33 34
163.3 169.8 176.j 183.4
21
99.5 104.8
22
110.2
23 24
121.2
20
cm .
T.
115.8
TABLE“B.” t.
P.
21.1
74.0
22.6 19.0 18.5
760.5 760.0 UNIVERSITY O F
26.2 26.5 26.0
21.4
748 4
V.
42.o 41.6 41.9 31.6 30.6
20.6
750.5 750.5 742 ’ 1 742 ’ 1 741 2 733.2 736.4
21 . o
6.2 50.2
49.6 41.7
(Cal.)
37.64 37 13 36.11 27.16 26.33 64’ 58 5.39 45.20 45.51 37.77
V (Obs.).
37.7
37.1 36.I 27.1
26,3 64.5 5.4 45.2 45 4 38.8
ILLINOIS,
C‘XBANA, ILL.
A LECTURE TABLE DOWN-DRAFT. BY Wna. L. DUDLEY. Received March 26, 1908.
A powerful and reliable down-draft on a lecture table is of great service and is much superior to a hood behind the lecturer since by its use experiments with the most disagreeable and poisonous gases can be made safely in full view of the audience. My experience in the past has been t h a t such down-drafts are rare, in fact, I have never had one t h a t was usable until I installed in the lecture theatre of Furman Hall, the new chemical laboratory, the arrangement herein described. The requirements of a good down-draft are ( I ) certainty of action regardless of the weather or temperature, ( 2 ) sufficient suction to permit of moderate freedom of action on the part of the experimenter which is not possible if the air current is so slow as to require a closed chamber to prevent the escape of gases into the room, (3) the draft tube with its cover being so arranged t h a t it can be located in or near the center of the lecture table flush with the table top so as to offer no obstruction, and (4) a cover to the draft tube which will not stick nor become fast from corrosion.
