Dec., I 9 I 6
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
SOME COMPARISONS OF METHODS FOR DETERMINING NITROGEN IN SOILS By W. I,. LATSHAW Received August 14, 1916
Since determinations of nitrogen in soils have been made b y t h e Kjeldahl method or some of its various modifications, considerable trouble has been experienced with t h e flasks bumping while distilling t h e ammonia from t h e digest. I n some cases t h e bumping is so violent t h a t flasks are thrown off t h e still. This is very annoying, especially when using glass flasks. Various means have been proposed t o meet the trouble as: ( I ) Distilling with steam; ( a ) Transferring digest t o a copper flask and allowing it t o bump, t h e danger of t h e flask breaking being eliminated. These methods answer t h e purpose, b u t ignore t h e real issue-the cause of t h e bumping. Furthermore, they are both laborious and consume considerably more time t h a n would a satisfactory method b y which t h e distillation could be made in t h e same flasks as t h e digestion. T o perfect a method of this nature, we had t o know t h e cause of t h e bumping. I n our regular work in which we diluted our digest t o 600 cc. before distilling. using 800 cc. flasks a n d t h e same amount of zinc as when we diluted t o loo cc. before distilling, we noticed t h a t very little bumping took place, while those diluted t o t h e less extent bumped considerably. Thus it would seem t o be a problem of diluting t h e heavy alkaline digest1 which consists of sand and a heavy voluminous precipitate of the metals in the soil which are precipitated by sodium hydroxide. TTe also decided t h a t if the heal-y metals in the soil were causing t h e trouble, t o add more in t h e form of mercury and mercuric oxide would cause more trouble, so t h e Gunning method was tried and comparison made with t h e Kjeldahl method using mercury, the same dilutions being made in each method. It was found t h a t where no mercury was used, there was no bumping. T h e Gunning method proved in every way satisfactory in respect t o eliminating t h e bumping, b u t required considerable time for digestion, in some cases as much as 4 or j hours. As this length of time was objectionable, a catalyzer was thought necessary and copper wire was used in 0.08 t o 0.1 g. amounts with excellent results. The time of digestion was reduced t o a n average of 2 ‘ 1 2 hrs. for each determination. XETHOD U S E D AT T H I S S T A T I O K
Place I O g. of soil in a n 800 cc.2 Kjeldahl flask with 7 g. of powdered sodium sulfate, approximately 0.08 t o 0 . I g. of copper wire and 3 5 cc. of pure concentrated sulfuric acid. Shake immediately t o prevent t h e soil from adhering t o the sides of t h e flask. Heat over a moderate flame, rotating or shaking occasionally so as t o secure even and complete digestion. Continue t h e digestion one hour after t h e solution becomes colorless. Cool and dilute with j o o cc. or more of water. Add a n excess of strong alkali and a small amount of 1 The principle of diluting the digest has been in use in this laboratory for the last five or six years and the author rlaims no credit for this idea. 2 Pyrex flasks were used exclusively in doing this work. We have found them superior to the well-known Jena flasks.
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zinc dust or granulated zinc, preferably t h e latter. Connect t h e flask with t h e distilling apparatus, mix thoroughly a n d distil, etc. I n order t o demonstrate more clearly the chemical efficiency of t h e method used a t this Station, t h e results of some experimental work are given in comparison with t h e Official Meth0d.l The results, given in Table I, show no marked differences in the two methods. TABLE I-COMPARISONOF PERCENTAGES NITROGEN BY
Sample 1383 1384 1385 1386 1387 1388 1389 1390 1091 1392 1393 1394
METHODUSED A T THISSTATION No. of Det’ns Max. Min. Av. 4 0.151 0 . 1 3 6 0.143 2 0.147 0.144 0.146 2 0.147 0.144 0.146 2 0.155 0 . 1 5 4 0.155 2 0.140 0.137 0.139 3 0.146 0.137 0.141 3 0.147 0.142 0.144 3 0.151 0.145 0.148 2 0.146 0.144 0.145 2 0.156 0 . 1 5 4 0.155 2 0.146 0.144, 0.145 2 0.147 0.146 0.147
TWO
METHODS
OFFICIAL METHOD No. of Det’ns Max. Min. Av. 3 0.145 0.142 0 , 1 4 4 3 0.147 0.145 0.146 2 0.148 0.146 0,147 2 0.160 0.158 0.159 2 0.143 0.139 0.141 2 0.143 0.140 0 . 1 4 2 ’ 2 0.142 0.140 0.141 2 0.146 0.143 0.145 2 0.144 0.143 0 , 1 4 4 2 0.153 0.153 0.153 2 0.142 0.140 0.141 2 0.146 0.145 0.146
As a means of showing t h e working efficiency of our method, some work may be described which was recently done with t h e aid of two student helpers, each working half time. We had 475 samples of soil t o analyze for nitrogen which, including duplicates and t h e blanks on several lots of alkali and several repeats, made approximately 1000 determinations. We used. one hundred and twenty 8 0 0 cc. Kjeldahl flasks and a I a-place block-tin condenser. Our average run was I O O determinations a day. Only two flasks broke, both of which fused dry in digestion. One of these broke after the distillation was completed. The other represents our sum total of losses in determinations due t o breaking of flasks. CHEMICAL LABORATORY, KAN5AS STATE AGRICULTURAL COLLEGE MANHATTAN, KAXSAS
THE DETERMINATION OF PHOSPHORUS PENTOXIDE AFTER CITRATE DIGESTION By 0 . C. SMITH Received June 27, 1916
Considerable difficulty is experienced b y most chemists in t h e digestion of t h e fertilizer and filter papers left after t h e removal of t h e reverted phosphate by t h e digestion with neutral ammonium citrate. The usual ‘method consists in the digestion with differing proportions of hydrochloric and nitric acids, preferably 30 cc. concentrated nitric and I O cc. concentrated hydrochloric. By this method a clear solution cannot be obtained with some fertilizers even after digestion for a whole day. By t h e use of t h e following method a clear solution can be obtained in less t h a n a n hour. Two grams of t h e sample are weighed on a filter paper in a funnel a n d washed with about Zjo cc. of water: t h e paper a n d sample are then transferred to a zoo cc. flask containing I O O cc. of neutral ammonium citrate, previously heated t o 60’ C. and heated a t 60’ with frequent shakings for l/z hr. The contents of t h e flask are then filtered immediately and washed with water a t 6 0 ” until all of t h e citrate solution and soluble phosphorus are removed. The two filter 1
“Soil, Total Nitrogen, Official,” .4. 0. A . C., No. 4, 1 (1916). IO.
