T H E JOUR,VAL OF I N D C S T R I A L A N D E;VGINEERISG C H E M I S T R Y
776
THE EFFECT OF GRINDING THE SOIL ON ITS REACTION A S DETERMINED BY THE VEITCH METHOD B y P. E. BROWNA N D H. W. Received April 16, 1915
JOHWSON
I n t h e course of some recent studies of Iowa soils, it became necessary t o ascertain their reaction or need of lime a n d inasmuch a s previous tests. h a d been carried o u t b y t h e Veitch method a n d comparisons h a d indicated it t o be quite satisfactory, it was decided t o use t h e same method in this work. I t mas soon noted, however, t h a t t h e results which were being secured were i n most cases t h e direct opposite of those obtained b y previous tests of samples of t h e same soil t y p e s t a k e n from approximately t h e same localities. For instance, practically all t h e samples f r o m Bremer County were found t o be basic i n reaction, whereas previous tests of t h e soils of t h a t c o u n t y h a d shown t h a t almost all were acid. The test h a d been carried out i n exactly t h e same way in b o t h cases. El-ery step in t h e operation a n d every detail i n manipulation was carefully checked b u t no difficulties were encountered with t h e method. T h e soil samples were t a k e n in t h e same way, a n d b o t h lots were chosen as representative of soil types. F u r thermore t h e y were t a k e n b y t h e s a m e man so t h a t there was every reason t o expect t h a t t h e reaction of t h e samples would be very similar. d t least i t w a s felt t h a t t h e same tendency of t h e soils t o react acid or basic should h a r e been observed with both lots of samples. There was only one difference in t h e two lots of samples: t h e first was secured especially for acidity tests a n d t h e soils were tested in a n unground condition: while t h e second lot was obtained in connection with t h e soil survey of t h e county a n d t h e samples were finely ground before being tested. This grinding was necessary in order t o prepare t h e samples for t h e chemical analysis which was t o be made of t h e soils. I t seemed probable, therefore, t h a t t h e difference in t h e reaction of t h e t w o lots of samples was due t o t h e grinding. T h e questions t h e n arose-Does the grinding of soils increase their basicity according t o t h e T'eitch t e s t ? If so: what causes t h e production of a basic reaction? I n a critical s t u d y of t h e method which he devised. T-eitch' observed t h a t t h e length of time t h e treated a n d dried soil was allowed t o s t a n d in contact with water h a d a considerable effect on t h e apparent acidity as determined b y t h e method. He noted t h a t when solution was allowed t o go on from q S t o i z hours t h e pink color with phenolphthalein was developed with less added lime water t h a n when t h e solution was allowed t o s t a n d 16 hours or less. T h e increase i n basicity was so pronounced in some cases t h a t soils which were acid when allowed t o s t a n d 16 hours gal-e a basic reaction upon standing 24 t o 4 8 hours longer. I n discussing t h e cause of t h i s increase in basicity, T'eitch concluded t h a t it was not due t o t h e failure of 1
J . .am. Chem. SOC.,26, 6 3 7 .
Vol. 7 > No. 9
C a C 0 3 t o go into solution in partially carbonated water in t h e shorter time a n d he suggested t h a t t h e cause might probably be found in t h e slower solubility a n d hydrolyzation of t h e neutral lime compounds t h a t are formed with t h e added lime water or t o t h e solution a n d hydrolyzation of neutral compounds already present i n t h e soil. H e called attention t o t h e fact t h a t in 1S4j, Rogers Brothers' showed t h a t m a n y of t h e common minerals, "particularly t h e zeolites a n d feldspars when reduced t o fine powder a n d t r e a t e d with carbon dioxide-free water, gave a more or less strong reaction with phenolphthalein." Since t h a t t i m e t h e solution of minerals i n water has been studied b y a large number of investigators* a n d it has come t o be quite generally accepted t h a t t h e observations of Rogers Brothers were correct. 1Iinerals are known t o be present in soils in considerable a m o u n t s , a n d their solution t o proceed very slowly. T h e development of a basic reaction when soils are subjected t o long standing in t h e lime-water test m a y ? therefore, be due t o t h e solution of silicates. T h e directions for carrying out t h e Yeitch test based on these experiments b y t h e a u t h o r of t h e method a n d numerous other investigators prescribe, therefore, t h a t t h e samples shall s t a n d only over night in contact with t h e water. I n t h i s way i t is deemed t h a t there is not sufficient time for t h e solution of a n y of t h e silicates in t h e soil t o occur a n d make t h e test basic. I t seemed probable t h a t the s a m e reason which T'eitch advanced for t h e development of a basic reaction b y soil upon long standing with water might account for t h e production of basicity i n a ground soil, t h a t is, t h e solution a n d hydrolyzation of silicates. As t h e point raised is of some interest a n d t h e question of t h e condition in which t h e soil should be when tested for acidity is of considerable importance, some tests have been carried o u t along t h i s line. X o previous investigations, as far a s t h e authors are aware. have specified what t h e condition of t h e soil should be when t h e 1-eitch test is applied, a n d these results indicate t h a t it is of importance because of t h e development of a basic reaction when soils are ground before being tested. E XP E RI ME K T .A L
In order t o determine definitely n7hetht.r grinding occasioned a development of basicity in soils. four samples of soil from Bremer C o u n t y were secured a n d each sample was thoroughly mixed a n d divided i n t o four portions. T h e first portion was unground a n d unsieved, t h e second was p u t through a 2 0 mesh siei-e, t h e t h i r d through a 40 mesh sie\-e a n d t h e fourth portion through a n 80 mesh sieve: grinding w a s done wherever necessary. I n t h e case of t h e Bremer fine sandy loam a n d t h e Carrington sandy loam very little grinding was necessary t o p u t t h e soils through t h e 20 mesh sieve b u t considerable grinding was needed t o p u t t h e m I 2
A m . J . Sci. and Arts. 6 (184.5). 5 . F. K. Cameron and J. M . Bell, Bur. of Soils, Bull. 90 (1905).
Sept
I Q Ij
---
T H E J O 1 7 R S . I L O F I S D c ' S l K I - I L . I s D E.VGISEEKISC; C H E M I S T R Y
through t h e 40 a n d 80 mesh sieves. With the other t w o soils, considerable grinding n-as required for t h e m t o pass t h e 2 0 mesh sieve. Examining t h e results gix-en in Table I , it is f o u n d t h a t all t h e soils shom-ed acidity when tested in an u n ground condition a n d all showed a basic reaction Tvhen t h e y were ground and p u t through an 80 mesh sieve before being tested. K i t h three of these samples enough basicity was de\-eloped. when t h e soils \\-ere ground t o pass the 40 mesh siei-e. t o change the reaction from acid t o basic. Even the slight grinding necessary to p u t t h e soils through the 2 0 mesh sieve reduced the lime requirements of tn-o of t h e soils. These results indicate clearly t h a t grinding i n creases t h e basicity of soils a n d those normally ha\-ing
, I 1
be expected. very little grinding being necessary t o p u t the fine s a n d y loam through the 40 mesh sieve. Xccording t o these results there seems t o he ii direct relationship betn-een t h e sand content of t h e soil and the effect 11-hich grinding t h e sample exerts on t h e reaction b y t h e Yeitch test. T h e larger t h e amount of sand present a n d the coarser the condition in which it exists. t h e less grinding is required t o alter t h e reaction of the soil according t o t h e 1-eitch test. TThere t h e percentage of sand is low t h e effects of grinding are small although the influence in reducing the lime requirement of acid soils is still noticeable. I t is evident, therefore. t h a t "silicatcs when tinely ground lead t o the de\-elopment of a basic reaction" in soils and t h e observations of Rogers Brothers a n d
TABLE I-REACTIONS .4So LIME REQUIREXGNTS :LBS P E R 2,000,000 LBS. O f S U R F . % C E S O I L ) O F FOCR S A N D Y I,0.4MS SOIL3-0.14 SOIL -No. 51 SOIL N o . 5 7 S O l L Y C J . 24 COKDITIOX O F S O I L Bremer fine sandy loam(u) Rremer coarse sandy loam ( b ) Rremer sandy loam(b1 Carrington sandy loarn(iil WHES TESTED Reaction Lime Reaction Lime Reaction Lime Reaction Lin:? Acid 5280 Unground a n d unsieved.. . . . . . . . . . . . . . . . . . . Acid 7816 .bid 3520 Acid 3168 Acid I i60 Acid 3520 .4cid .3 168 Through 20 mesh s i e v e . , . . . . . . . . . . . . . . . . ..4cid 2816 Basic Basic Basic Through 40 mesh sieve.. . . . . . . . . . . . . . . . . Acid 2116 Through 80 mesh S k y e . . . . . . . . . . . . . . . . . Basic Basic .... Basic Basic ! b ) Considerable grinding t o p a % 2 0 mesh ( u ) Very little grinding t o pass 20 mesh.
a n acid reaction b y t h e Yeitch test m a y show a basic reaction. In order t o test t h e point further a n d also t o ascertain t o what extent t h e sand affected the development of a basic reaction when a ground sample was tested, fix-e samples of t h e Lintonia series of soils from 1Iuscatine C o u n t y , Iowa, carrying different contents of s a n d a n d all reacting acid in t h e natural condition were tested in t h e same way as t h e prei-ious soils. T h e results appear in Table 11. The coarse sand needed a little grinding t o p u t it through t h e 2 0 mesh siei-e a n d this reduced t h e lime requirement somewlint b u t when ground and p u t 5011, S O . 37 Coarse sand(a) Q2.2C; sand CONDITION O f S O I L IYHEN TESTED Reaction Lime Lngroond and uniievt,d.. .Acid ,5280. 0 Through 70 mesh sieve . .Acid 4224.0 Basic .. Through 10 mesh sieve . . Through 80 mesh s i e v e . . . Basic .. i u ) Little grinding to pa55 20 mesh. (1,) Vm>- littlc grinding t o pass 20 mesh.
SOIL N o . 3 7 Find sandfh) Y2.0C; Acid ,501 . 7 Acid ,501 7 i Acid 4348 i
I. I
reaction should lbe determined n-itliout consideration of thc presence of silicates. S U 11 11.4 R 1
The results of these tests lend t o the following i o n clusions: I-When acid soils are ground liefore heing tested b y t h e 1-eitch method t h e acidity is reduced and frequently t h e reaction becomes basic. 11-The development of basicity increases with t h e grinding of t h e soil. 111-The increase in basicity depends upon t h e a m o u n t of sand present and is greater in coarse sandy soils t h a n in fine sands. IV--Soils should not be ground previous t o testing their reactions by the T-eitch method. LABOR.\TORY O F S O I L C H E X I S T R Y A X V BACTERIOLOGY IOWASTATE C O L L E G E , AMES
