When distilling nitric acid from thc usual mixture of sodium nitrate and sulphuric acid, it is frequently observed that a t certain periods a ~ i o l e i i t reaction sets in, :md that the coiitonts of t h e retort are carried over i n the receivers. 'l'lie general supposition is t h a t its cause is overheating, and t u lireyent it, the distillatioii is carried on a t a low tcniperatuw, and the retorts are made of such capacity t h a t tlie foaming may s p m d itself without reaching t h e conductiiig tube and i,uiining ovcr. Howevt:r, I t can be observed that t h e foaming of the retort contents occiirs a t certain periods of thc continuation of the process, even when only a very niodcrato heat is applied, and is therefore dependent not merely upon its external application; arid its it does appear that the distilling acid linx i i close connection with the reaction taking place in the retort, i l l rclation to boiling point and constitution, a consideration of the q u a l i t i ~ sof nitric acid of different concentrations will serve i i i the explanation of these differe n t reactions, especially during the distillation of t,he acid from the mixture of sodium nitrate and s u l ~ ~ l i u racid. ic A. Smith 1 fourid t h a t a nitric ircid of theconstant boiling point S1,56"U liad i~ specific gravity of 1.5W-1.51, and was tlie first hydrate, K O , H O or TISO,; also that ail acid, boiling coustantly ; I t l z l - , had tlie specific gravity 1.41 a u d wis the second hydrate, NO 2 IIO or X 0 '2 IJ 0. Eoscoe 2 states, that by boiling iiitric acid of any concentration, a rcsidnc of constant specific gravity 1.11 and boiling poilit 120.5" remains: tliis seems t o correspond with Smith's second hydrate. T'he existencc of definite hydrates of nitric &cid has been questioned freyueiitly, but the corresponding boiling points and specific ~
1 2
. ...
. . . . ..
..
A. Smith, Phil. Mugnzine (3) 31, p. 434. Roscoe. Jnhresber.icht 18F0, p. 63.
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___
T H E DECOMPOSITION O F SODIUM NITRATE.
247
gravities, as well as some reactions in the decomposition of nitrates in presence of water, and the fact t h a t not only anhydrous nitric acid, but also the hydrates, when brought in contact with water, develop heat, cannot' very well be explained except upon tlie theory t h a t several chemical combinations with water exist. Discrepancies in boiling points as well as in specific gravities are always likely t o exist, also, the first and second hydrate are constantly decomposing, especially under the influence of light, and this cannot therefore be held as a valid objection to the theory of digtinct hydrates. In tlie preparation and manufacture of nitric acid, the processes and reactiors can best be explained by t h e acceptance of the several hydrates of nitric acid, and the following table of observations furnishes n direct proof of it. I concluded t o conduct the experiments with, comparatively speaking, large qnantities, and as I had fiicilities for obtaining strong acid for the preparation of nitro-compouuds and organic nitrates, I had occasion to repeat my obsorvatioris. T h e table thereof, which I give here, refers to the distillation of t h e acid from a mixture of 2500grms. sodium nitrate and 2600grms. of commercial sulphuric acid of 1.837 specific gravity a t 67" F. T h e tubulated glass retort had'a capacity of about two gallons, was provided with a thermometer in the tubulus and 1)eated in a parafine bath the temperature of which could also be ascertained by thermometer. T h e bulb of the inside thermometer did not reach t h e iixture in the retort and indicated the temperature of the distilling zpors. T h e condensation wac effected by a Liebig's condenser, .{hereby a n exchange of receivers was rendered easy. I noted, during the distillation, the time, t h e temperature, as indicated by the in- and outside thermometer, and the quantities of acid received in different periods; the reactions of the contents of t h e retort were also observed. These notes arc contained in t h e following: Time.
--TemperatureOutside. Inside.
A. M. 10.10
83"
11.30 11.45
S5O 90"
45" 47" 50"
94 "
52O
Remark.
Reaction commences. Gas forming; mass caking. s
i
'(
ii (i
248
T H E I)ECOMPOSITION O F SOIJJV'lf S I T R A ' l ' E .
Time.
A. M. 11.45 11.53
,-Temperstu re-Outside. Inside.
97 " 102" 10G" 110.'
118'
55" 38.) G5" 70" 75" 6 IC 1, '
120"
A
Noon. 12.00
122"
80"
I?. M. 12.10
122"
81"
12.15
122"
81"
12.1G
122"
81"
12.16
122"
81"
12.20
120"
80"
118O 115"
80" 81"
12.30
117"
88"
12.47
118"
88"
1.00 1.10
120" 122"
90" 90"
1-37 1.45 2.00
125" 130' 130'
90" 99" 90"
2.10
131'
90"
2.20
131" 130"
90" 94"
2.45
Hcmarks.
Gas forming, mass caking. i'
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