IO44
T H E J O U R N A L OF I N D U S T R I A L A N D ELVGINEERING C H E M I S T R Y
in general, effects somewhat more beneficial t h a n the highly magnesian dressings. 5-The yields from t h e hydrate applications all exceeded those from t h e corresponding carbonate a p plications, t h e average for t h e former being 2.62 as contrasted with 2 . 2 1 for t h e carbonates, exclusive of dolomite. 6-The dolomite was beneficial, b u t less so t h a n the corresponding dressing of calcite a n d magnesite. E F F E C T S UPOK A S H C O M P O S I T I O K
T o determine in what measure t h e clover plants consumed t h e lime a n d magnesia t h u s supplied, t h e crops (tops) were analyzed, with t h e results given in Table I. The figures show t h a t : I-All t h e treatments increased t h e proportion of ash in t h e plants, t h e dolomite least, t h e hydrate most. a-From dolomite, t h e plants took u p less ash for each unit of d r y matter increase, t h a n did those receiving t h e other dressings. T h e CaO : MgO ratio of t h e ash increase was, however, 3 . 4 : I ; t h a t is, from t h e dolomite t h e plants took calcium far more freely t h a n magnesium. 3-From t h e other dressings, t h e plants took u p magnesium much more freely t h a n from t h e dolomite. F r o m t h e low-calcium dressings t h e y took proportionally more magnesium t h a n t h e y did from t h e most highly calcareous, dressings-speaking with reference t o molecular proportions. 4-The crops took relatively a little more magnesia t h a n calcium from t h e hydrate v s . t h e carbonate dressings. 5-In general, t h e plants were not self-protected b y a n exclusion of t h e magnesia. It entered t h e m , a n d , judging from t h e yields as compared with t h a t obtained from t h e use of purely calcareous limestone, did t h e m no detectable h a r m , except slightly delaying t h e germination. I n no case, however, did t h e percentage of magnesia in t h e ash reach t h e amount stated b y Wolff' for fully ripe clover, although for most of t h e treatments it exceeded t h e amount he gives for this plant a t t h e time of bloom. DEPARTMENT OF EXPERIMENTAL AGRICULTURAL CHEMISTRY STATECOLLEGE PENNSYLVANIA STATECOLLEGE, PA.
A NOTE UPON THE KJELDAHL METHOD FOR NITROGEN DETERMINATION By PHILIPL. BLUMENTHAL AND G. P. PLAISANCE Received May 17, 1915
I n a recent number of THIS J O U R K A L , Picke12 quoted results upon various substances analyzed b y t h e Kjeldahl-Gunning-Arnold method, in which he heated t h e sample from 15 minutes t o 3 hours. He stated t h a t 30 minutes total heating gave excellent results. T h e writers, while engaged in analyzing t h e carcasses of new-born pigs, experienced some little difficulty in obtaining concordant results b y different methods in general use, a n d finally conducted a short series of analyses under varying conditions, t o ascer1
Aschen Anolysen, I (1880). 122.
2
THISJOURNAL, 7 (1915). 357.
Vol. 7, No.
12
tain t h e maximum nitrogen yield. As a check upon t h e accuracy of t h e results, a sample of very pure casein (Hammarsten's) was analyzed at the same time. Table I shows t h e results obtained upon t h e animal carcasses, digesting for j- a n d 3-hour periods after the solution became clear. T h e Kjeldahl-Gunning-Arnold a n d t h e GunningCopper sulfate digestions cleared more quickly t h a n those of t h e other methods tested, a n d were deemed preferable for t h e further tests. I n t h e second series (Table 11) casein a n d t h e pig sample were heated for various lengths of time a n d t h e results recorded. A glance a t these tables shows t h a t 30 minutes' total heating does not suffice t o fix all t h e nitrogen; in fact, a gain of over 3 per cent protein is obtained b y a longer period of digestion. . T h a t this is not due t o a n error is evidenced b y t h e figures on casein, in which t h e percentage of nitrogen is I j.68. T h e conditions followed were quite similar t o those proposed b y Pickel, except t h a t it was necessary t o a d d more sulfuric acid t o prevent t h e solidification of t h e flask contents in t h e long digestions; in every case, therefore, j o cc. of concentrated sulfuric acid were used a t t h e start. I t does not seem satisfactory t o us t o rely upon a definite time of total h e a t i n g , because of variations in gas pressure, a n d in t h e efficiency of differe n t burners. We prefer t o heat for a definite length of time after clearirtg, a n d from t h e results quoted, this time should never be less t h a n one hour. An interesting point came t o our attention during t h e work. M a n y chemists have noticed t h e formation of a black material, which tends t o accumulate in t h e condensers a n d adapters of t h e distillation rack. Sometimes (where paraffin is used in digestion or distillation) this material is greasy or salve like. It was noticed t h a t where this material was carried over into t h e receivers, higher results were obtained t h a n with other determinations of t h e same set. T h e black deposit contains mercury a n d often paraffin: sometimes mercury globules are observed in t h e receivers.' We believe t h a t this m a y be explained as follows: mercuric sulfate treated with a considerable excess of potassium sulfide a n d sodium hydroxide is first precipitated as mercuric sulfide, which is later partially or completely dissolved as a complex salt. T h e clearing of t h e dark-colored flask contents in boiling, a frequent occurrence, substantiates this view. Zinc is generally added t o prevent bumping a n d t h e hydrogen generated b y its reaction with sodium hydroxide, particularly when excess of these reagents is used, tends t o liberate metallic mercury. This is fairly volatile at t h e temperature of t h e boiling solution, a n d paraffin may also be carried over under these conditions; t h e result is t h e black substance mentioned, which is quite difficult t o remove from t h e condensers, a n d which is objectionable, even if no chemical action occurs with t h e ammonia liberated from t h e solution, or with t h e acid in t h e receiver. B y substituting bits of unglazed porcelain or pumice, t h e bumping of t h e solution is decreased, a n d though these substitutes are not quite so efficient in preventing 1
Bosshard, 2. a n d . Chem., a4, 199; also Pickel, see above.
Dec., 1 9 1 5
TABLE I-COMPARISON OF METHODSUSED Digested 5 hrs. after clear Method No. of P e r cent nitrogen number METHODUSED detns. Max. Min. Av. 1 Kjeldahl (modified) Official: 5Occ. H z S O ~ 0 . 7 g . H g KMnOa.. .......................... 4 8.38 8.34 8.36 2 Kjeldahl (modified) Official: 30 cc. H2SOa 0.7 e. He 5 8.45 8.38 8.41 - 20 cc. HzS04 (added later) K M n 0 4 . . 3 Kjeldahl-Gunning-Arnold,modified b y using K M n 0 4 and excess HzS04: 50 cc. HsSOa 0 . 7 g. H g 10 g. KzSO4 KMnOa.. . . . . . . . . . . . . 5 8.10 7.95 8.04 ' 4 Kjeldahl-Gunning-Arnold, modified b y using KMOna a n d excess HzSO4: 30 cc. HzSOa 0 . 7 g. H g 10 g. K&Oa 20 cc. H ~ S O (added I later) KMnOa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 8.29 8.20 8.26 Kjeldahl-Gunning-Arnold, modified b y using excess HzSOa (no KMnOa) : 5 3 0 c c . H & O a + 0 . 7 g . H g + 10g.KzSOa + 2 O c ~ . H z S O a ( a d d e d l a t e r ) . 5 8.28 8.19 8.22 6 Kjeldahl-Jodlbauer (Official Kjeldahl t o include nitrates) : 50 cc. H?SO4 0.7 g. H g 2 g. salicylic acid 2 g. Z n d u s t KhZnOa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 8.29 8.18 8.23 7 Kjeldahl-Gunning-Jodlbauer: 50 cc. H 6 O a 0 . 7 g. H g 2 g. salicylic acid 4- 2 g. Z n dust 10 g. K2SOa KMnOa.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 8.28 8.16 8.24' 8 Dyer's modification of Kjeldahl-Gunning-Jodlbauer: 50 cc. H&Oa 0 . 7 g. H g 2 g. salicylic acid 2 g. Zn d u s t 10 g. KzSOa 1 E. sucrose KMnOa., . . . . . . . . . . . . . . . . . . . . . . . . 6 8.33 8.21 8.27 9 Gunning-Copper sulfate (modified b y using K M n O 4 : 50 cc. HzSO; 0 . 2 g. CUSOI f 10 g. KzSOa KMnOr., . . . . . . . . 5 8.41 8.04 8.23 I O Gunning-Copper sulfate: 50 cc. H2SOr 0 . 2 g. CuSOa 10 g. KzSOc.. . . . . . . . . . . . . . . . . . . 5 8.26 8.25 8.25 11 Official Gunning: 50 cc. H ~ S O I 10 g. KzSOa,, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 8.27 8.09 8.17 12 Panadium-Gunning: 50 CC. H2SOa 10 g. KzS04 0 . 2 g. VzOs(a). . . . . . . . . . . . . . . . . . . . . . . . .... .... ( a ) E z p e r i m e n f S f a t i o n R e c o r d , 32, 310.
+ + + +
+ +
+
I045
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
+ +
+
++
++
+
+ +
+ + ++
+ +
+
+ +
+ + +
+
+
+
+
Digested 3 hrs. a f t e r clear Per cent nitrogen Max. Min. Av.
No. of
detns. 5
8.30
8.22
8.26
2
8.34
8.32
8.33
2
8.15
8.14
8.14
.. ..
....
....
....
....
.... ....
..
....
....
....
....
....
..
. . t .
3
8.28
8.27
8.27
5
8.30
8.20
8.24
.. ..
.... ....
....
....
.... ....
6
8.12
7.96
8.06
TABLE11-PERCENTAGE h T I T R O G E N I N CASEIN A N D P I G S B Y DIFFERENT TREATMENTS NITROGENIN LOTI1 PIGS h-ITROGEN I N L O T 11 P I G S SITROCEN IN CASEIX Gunning-Copper Sulfate Kjeldahl-Gunning-Arnold K j eldahl-Gunning-Arnold TOTAL HEATIXC Hours heating TOTAL HEATING Hours heating TOTAL HEATING Hours heating Minutes after clearing(a1 Minutes after clearing(b) Minutes after clearing(h) 30 45 60 1 3 5 15 30 45 60 1 3 5 15 30 45 60 1 3 5 NUMBER 15 1 A 13.23 13.89 14.20 14.46 1 4 . 5 6 1 4 . 6 4 14.39 7 . 3 2 8.06 8.06 7 . 9 1 8 18 8 . 3 2 Lost 7.33 7.63 7 . 7 0 7 . 9 4 8 . 1 3 8 . 2 0 8 . 4 4 B 13.36 13.87 14.62 14.49 7 . 2 5 8 . 0 5 7.97 7 . 8 8 8 . 1 7 8 . 3 4 8 . 4 6 7.77 8.26 8.37 2 C 13.39 13.96 14.24 1 4 . 4 4 14.53 1 4 . 5 7 1 4 . 4 1 7 . 5 9 7 . 7 1 8 . 1 6 8 . 1 3 8 . 2 0 8.37 8 . 4 3 7.34 7 . 6 4 7 . 7 7 7 . 9 2 8 . 1 1 8.27 8 . 3 7 D 13.49 Lost 14.67 14.54 7 . 5 8 7 . i 3 8 . 1 5 8.12 8 . 2 3 8.37 8 . 4 6 7.77 8.30 8.38 AVER. 13.37 13.91 1 4 . 2 2 14.45 14.55 1 4 . 6 2 1 4 . 4 6 7 . 4 4 7 . 8 9 8 . 0 9 8 . 0 1 8 . 2 0 8 . 3 5 8.45 7 . 3 4 7 . 6 4 7.75 7 . 9 3 8 . 1 2 8 . 2 6 8 . 3 9 DETERMINATION : METHOD:
14.41 15.00 15.33 1 5 . 5 8 1 5 . 6 8 15.77 15.60
..............................................
aver. ( a ) 35 minutes were required until clear.
( b ) 70 minutes were required until clear.
bumping, t h e usual frothing resulting from t h e use of zinc is obviated, a n d a t t h e same t i m e the distillation of mercury is eliminated. We experienced no further contamination of t h e condensers or re, ceivers a f t e r making this change. CHEMICAL SECTION IOWA AGRICULT~RAL EXPERIMENT STATION AMES,IOWA
METHODS FOR THE DETERMINATION OF CARBON DIOXIDE AND A NEW FORM OF ABSORPTION TOWER ADAPTED TO THE TITRIMETRlC METHOD' B Y E. TRUOG Received April 22, 1915
A large number of different methods and f o r m s of apparatus have been recommended for t h e d e t e r m i n a tion of carbon dioxide. This is largely due t o t h e f a c t t h a t t h e determination is made for a large variety of purposes a n d under numerous different conditions. I n t h e chemical analyses of soils a n d i n t h e investigation of soil phenomena, t h e writer has had numerous occasions t o determine carbon dioxide. I n such work carbon dioxide is usually determined by one of t h e three following methods: gas-volumetric, gravimetric, a n d titrimetric. I n order t o s'ecure sufficiently accurate results f o r most purposes with t h e gas-volumetric method, rather elaborate apparatus is usually required, a n d hence t h e method is not used as generally as t h e others. 1 Publication authorized b y t h e Director of t h e Wisconsin Experiment Station.
T H E GRAVIMETRIC METHOD
The gravimetric method, in which t h e carbon dioxide is absorbed in a KOH bulb or other'absorbing tubes, gives very accurate results when t h e large number of precautions are strictly observed. These precautions a n d t h e disadvantages of t h e gravimetric method have been very completely set forth by J . R. Cain.' A precaution often ignored. b u t of great importance, is in the use Of drying reagents Of the Same hygroscopicity a t both ends of t h e COS absorption bulb. The air must be dried t o exactly t h e same degree, both when it enters a n d leaves t h e absorption bulb, or there will be a n error due t o loss or gain of water. I n t h e writer's experience errors from this source may amount t o as much as t w o milligrams. I n t h e case of rapid aspirations of large volumes of gas so much absorbing a n d drying apparatus is needed t h a t errors in weighing become serious. THE ALKALI TITRIXETRIC METHOD
oITTingto disadvantages of t h e gravimetric method, \.arious titrimetric methods have into use. of these methods t h e absorption of t h e carbon dioxide in a sodium or potassium hydroxide solution a n d determination of t h e carbonates by double titration with phenolphthalein and methyl orange has been the most m7idely used. hi^ method for the absorption and determination of free carbon dioxide was first used b y Brown a n d Escombe.2 These investigators apparently 1 Technological Paper, 33, Bur. S t a n d a r d s ; also THIS JOURNAL,6 (1914). 465. 2 Phil. Trans.. (23)193 (1900). 289.
