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On the carbonic acid content of the atmospheric air
Scientific Notes and Comments.
240
[ J. F. I.,
CHEMISTRY. ON THE CARBONIC ACID CONTENT OF THE ATMOSPrtERm AIR.
By R,
Blochmann(Ann. 2 3 7 , 3 9 - 9 o ) . ' T h e above paper combines a thorough t o m parative study of the methods employed a n d the experiments performed up to the present time, for the purpose of d e t e r m i n i n g the a m o u n t of carbonic acid contained in the air, with a n account of the modification a n d improvem e n t by the author of the Dalton-Pettenkofer m e t h o d for d e t e r m i n i n g atmospheric carbonic acid. Considerable space is devoted to the discussion of the sources of error, to which the various methods heretofore employed are subject, a n d attention is called to the fact that as more refined methods came into use, a n d more care was t a k e n to determine a n d eliminate errors of experiment, the srrialler the accepted figure for the a m o u n t of CO 2 in the air became. Thus : NUMBER OF-PRR~ODS.
I828 to I83o i83o " 1856 x856 ,, x885
!
ob (S.u.~.ro) ........ ..6'
I1> Ob..... ,.o~o .o. ,i.... 3.~
Vol. C02 in xo,ooo Vo|. Air.
4"1[ 3"6 3"x
Of all the methods hitherto used for d e t e r m i n i n g the c a r b o n dioxide of the air, the so-called Pettenkofer method, on account of its simplicity and rapidity, was chosen by the author as the one whose imperfections could be dealt with with the greatest hope of success. T h e principle of the m e t h o d is this, viz., into a large glass bottle c o n t a i n i n g . t h e air to b e examined, is run a measured, quantity of s t a n d a r d b a r y t a water. T h e bottle is then corked and s h a k e n , a n d the b a r y t a solution transferred to a suitable vessel, titrated with s t a n d a r d acid, a n d the excess determined. T h e principal sources of error are, first, the absorption of CO2 by the b a r y t a solution from the air of the room during the titration. Second, in washing the bottle with hot water, more or less decomposition of the glass occurs, r e n d e r i n g the solution more alkalin ,e~ Third, in the use of caoutchouc stoppers, which, in accordance with n u m e r o u s observations, w h e n in contact with alkaline liquids, undergo oxidation, with the liberation of carbon dioxide. T h e first of these difficulties h a s b e e n met b y the e m p l o y m e n t of a c o m p o u n d burette, communication between the two halves of which is effected by m e a n s of a three-way glass stop-cock. In this piece of apparatus, both the acid a n d the b a r y t a solution to be determined, m a y be m e a s u r e d a n d titrated out of contact with the air, with the greatest accuracy. T h e second of the above operations h a s been r e n d e r e d unnecessary. In order to avoid the use of caoutchouc, the neck of the bottle is fitted with a stopper, consisting of a well-fitting glass-plate, a layer of mercury, a n d then a layer of paraffin, the whole b e i n g b o u n d down by a piece of sheet-rubber. T h r o u g h the stopper pass two glass-tubes with stout walls, a n d supplied with glass stop-cocks. One of the tubes reaches to the bottom of the battle,
Scientific'Notes and Comments.
Mar., I887.]
241
The sum of the constant errors affecting any result by this method is '1o and the probable error of a single experiment lies between + o'o2 5. The following table contains estimations of the carbon dioxide in the air from the laboratory garden, KSnigsberg :
DATES.
I I885, September
4 5
"
"
"
"
io
,c
Bottle No. 95Vol. CO2 in io, ooo Vol. Air.
Bottle No. 64. Vol. CO2 in xo coo Vol. Air.
9
,,
cc
'"
ii
~,
.
13
12
lI
Mean.
I
3"09 3~4
3"iz 3'24
3.]o 3 24
3'I0 3'09 3"*9
3'~3 3 08 3"z5
3'If 3'08
3"*5 2 05 [ 2"9r 3 u6 '
3 "I8 3'o0 296 3 I'3 3"o9
3'z7
306 3"25 3"H 3'07 3*9 3u5 "98 ~94 3']4 3'o3
3"06
3"17 2 97 2'93 3"4
3"07
.
[ I Joint Mean.
lI
Mean.
3'1~ 3'26 3'*z 3'°9 3":8 3"-W 2"98
3.08 3"~5 3"~i 3 08 3"i8 3 I6 2'98
2"95
2"95
3"x5 3'05
3'*5 3"o5
] / . /
3'*0
[
.
.
y*o
[ ] [
• 3'o9 3"25 3"n 3"o8 3"x8 3'x6 2"98 2'94 3"*5 3"°6 3"Io
A. G. P. A NEW REACTION FOR THE DETECTION OF SMALL QUANTITIES OF HYDRO-
CYANIC ACID.--G. Vortmann (Mona[schefte, 7, 416,) states that Playfair's reaction of the cyanides and nitrites is an exceedingly delicate test for a cyanide or hydrocyanic acid, the resulting nitro-prusside being recognized by its reaction with sulphides. The liquid to be tested is mixed with a few drops of potassium nitrate solution, from two to four drops of ferric chloride solution, and enough dilute sulphuric acid to change to bright yellow the first formed yellow-brown color of the basic iron salt. The mixture is heated until it begins to boil, then allowed to cool, and after the separation of the excess of iron a few drops of ammonia are added; the liquid is filtered and the filtrate treated with one or two drops of a much-diluted solution of colorless ammonium sulphide. The presence of hydrocyanic acid in the liquid will now occasion a beautiful violet color, changing in a few minutes to blue, then to green and yellow. Traces of hydrocyanic acid occasion only a bluishgreen color, that rapidly becomes yellowish. The limit of the reaction is put at a dilution of I :312,5oo, ten cubic centimetres of liquid being used; the limit of the Prussian blue reaction is I : 5o,ooo; that of the ammonium rhodanate I :4,000,00o. W.H.G. A NEW EXPLOSIVE MIXTURE.--A. Cavazzi (Gazzetta Chimica ltaliana), in studying the reduction of potassium nitrate by various substances, has found that a mixture of equal parts of the nitrate and sodium hypophosphite detonates violently when heated to about the fusing point of the mixture. The experiment should be made on small quantities only,'and while other proportions yield an explosive mixture, those mentioned are the best. • W.H.G. DETERMINATION
lung. I886.
OF FAT
IN MILK,
ETC.
M. Kretzschmar.
(Chem. Z e i -
IOO.)--A gravimetric determination of fat in milk and other
240
[ J. F. I.,
CHEMISTRY. ON THE CARBONIC ACID CONTENT OF THE ATMOSPrtERm AIR.
By R,
Blochmann(Ann. 2 3 7 , 3 9 - 9 o ) . ' T h e above paper combines a thorough t o m parative study of the methods employed a n d the experiments performed up to the present time, for the purpose of d e t e r m i n i n g the a m o u n t of carbonic acid contained in the air, with a n account of the modification a n d improvem e n t by the author of the Dalton-Pettenkofer m e t h o d for d e t e r m i n i n g atmospheric carbonic acid. Considerable space is devoted to the discussion of the sources of error, to which the various methods heretofore employed are subject, a n d attention is called to the fact that as more refined methods came into use, a n d more care was t a k e n to determine a n d eliminate errors of experiment, the srrialler the accepted figure for the a m o u n t of CO 2 in the air became. Thus : NUMBER OF-PRR~ODS.
I828 to I83o i83o " 1856 x856 ,, x885
!
ob (S.u.~.ro) ........ ..6'
I1> Ob..... ,.o~o .o. ,i.... 3.~
Vol. C02 in xo,ooo Vo|. Air.
4"1[ 3"6 3"x
Of all the methods hitherto used for d e t e r m i n i n g the c a r b o n dioxide of the air, the so-called Pettenkofer method, on account of its simplicity and rapidity, was chosen by the author as the one whose imperfections could be dealt with with the greatest hope of success. T h e principle of the m e t h o d is this, viz., into a large glass bottle c o n t a i n i n g . t h e air to b e examined, is run a measured, quantity of s t a n d a r d b a r y t a water. T h e bottle is then corked and s h a k e n , a n d the b a r y t a solution transferred to a suitable vessel, titrated with s t a n d a r d acid, a n d the excess determined. T h e principal sources of error are, first, the absorption of CO2 by the b a r y t a solution from the air of the room during the titration. Second, in washing the bottle with hot water, more or less decomposition of the glass occurs, r e n d e r i n g the solution more alkalin ,e~ Third, in the use of caoutchouc stoppers, which, in accordance with n u m e r o u s observations, w h e n in contact with alkaline liquids, undergo oxidation, with the liberation of carbon dioxide. T h e first of these difficulties h a s b e e n met b y the e m p l o y m e n t of a c o m p o u n d burette, communication between the two halves of which is effected by m e a n s of a three-way glass stop-cock. In this piece of apparatus, both the acid a n d the b a r y t a solution to be determined, m a y be m e a s u r e d a n d titrated out of contact with the air, with the greatest accuracy. T h e second of the above operations h a s been r e n d e r e d unnecessary. In order to avoid the use of caoutchouc, the neck of the bottle is fitted with a stopper, consisting of a well-fitting glass-plate, a layer of mercury, a n d then a layer of paraffin, the whole b e i n g b o u n d down by a piece of sheet-rubber. T h r o u g h the stopper pass two glass-tubes with stout walls, a n d supplied with glass stop-cocks. One of the tubes reaches to the bottom of the battle,
Scientific'Notes and Comments.
Mar., I887.]
241
The sum of the constant errors affecting any result by this method is '1o and the probable error of a single experiment lies between + o'o2 5. The following table contains estimations of the carbon dioxide in the air from the laboratory garden, KSnigsberg :
DATES.
I I885, September
4 5
"
"
"
"
io
,c
Bottle No. 95Vol. CO2 in io, ooo Vol. Air.
Bottle No. 64. Vol. CO2 in xo coo Vol. Air.
9
,,
cc
'"
ii
~,
.
13
12
lI
Mean.
I
3"09 3~4
3"iz 3'24
3.]o 3 24
3'I0 3'09 3"*9
3'~3 3 08 3"z5
3'If 3'08
3"*5 2 05 [ 2"9r 3 u6 '
3 "I8 3'o0 296 3 I'3 3"o9
3'z7
306 3"25 3"H 3'07 3*9 3u5 "98 ~94 3']4 3'o3
3"06
3"17 2 97 2'93 3"4
3"07
.
[ I Joint Mean.
lI
Mean.
3'1~ 3'26 3'*z 3'°9 3":8 3"-W 2"98
3.08 3"~5 3"~i 3 08 3"i8 3 I6 2'98
2"95
2"95
3"x5 3'05
3'*5 3"o5
] / . /
3'*0
[
.
.
y*o
[ ] [
• 3'o9 3"25 3"n 3"o8 3"x8 3'x6 2"98 2'94 3"*5 3"°6 3"Io
A. G. P. A NEW REACTION FOR THE DETECTION OF SMALL QUANTITIES OF HYDRO-
CYANIC ACID.--G. Vortmann (Mona[schefte, 7, 416,) states that Playfair's reaction of the cyanides and nitrites is an exceedingly delicate test for a cyanide or hydrocyanic acid, the resulting nitro-prusside being recognized by its reaction with sulphides. The liquid to be tested is mixed with a few drops of potassium nitrate solution, from two to four drops of ferric chloride solution, and enough dilute sulphuric acid to change to bright yellow the first formed yellow-brown color of the basic iron salt. The mixture is heated until it begins to boil, then allowed to cool, and after the separation of the excess of iron a few drops of ammonia are added; the liquid is filtered and the filtrate treated with one or two drops of a much-diluted solution of colorless ammonium sulphide. The presence of hydrocyanic acid in the liquid will now occasion a beautiful violet color, changing in a few minutes to blue, then to green and yellow. Traces of hydrocyanic acid occasion only a bluishgreen color, that rapidly becomes yellowish. The limit of the reaction is put at a dilution of I :312,5oo, ten cubic centimetres of liquid being used; the limit of the Prussian blue reaction is I : 5o,ooo; that of the ammonium rhodanate I :4,000,00o. W.H.G. A NEW EXPLOSIVE MIXTURE.--A. Cavazzi (Gazzetta Chimica ltaliana), in studying the reduction of potassium nitrate by various substances, has found that a mixture of equal parts of the nitrate and sodium hypophosphite detonates violently when heated to about the fusing point of the mixture. The experiment should be made on small quantities only,'and while other proportions yield an explosive mixture, those mentioned are the best. • W.H.G. DETERMINATION
lung. I886.
OF FAT
IN MILK,
ETC.
M. Kretzschmar.
(Chem. Z e i -
IOO.)--A gravimetric determination of fat in milk and other