INDUSTRIAL AND ENGINEERING CHEMISTRY
May, 1927
also been plotted to illustrate the nature of the results obtained (Figure 4). Extent of Hydration during Soaking
In order to determine to what extent the hydration proceeds in the overnight soaking in the form of putty, which the hydrate should receive before use, a sample of hydrate No. 16 was soaked for 24 hours as a putty of about the consistency ordinarily employed, dried a t 110”C., and then subjected to a thermal analysis in the same manner as the others. A comparison of the data with that from hydrate No. 17 ( S o . 16 before soaking) shows that a considerable amount of hydration does take place in soaking the material overnight. The percentage of magnesium oxide as hydroxide has increased to an appreciable extent and the percentage of CaO other than as carbonate or hydroxide has become practically negligible. Since, as in practice, no attempt‘ was made to exclude carbon dioxide, its percentage has also increased to a considerable degree. This test is by no means conclusive, however. As the sample was dried a t 110” C., it is possible that the increased hydration may have taken place during this operation rather than during the 24 hours’ soaking. Even with this treatment the magnesium oxide not present as hydrate amounted to more than 50 per cent of the total. Discussion of Results
I n considering the results as shown in Table 111, the low percentages of magnesium oxide combined as hydroxide in samples S o s . 11 to 16 and the comparatively high percentages in Nos. 23 to 103 may be explained by the fact that the second qeries had been in the laboratory for some time and, although
629
kept tightly closed, these samples have doubtless absorbed a certain amount of atmospheric moisture. Nos. 11 to 16 were freshly received from the manufacturers. The calcium oxide of all samples, with the possible exception of Nos. 11, 13, and 52, seems to be almost completely combined in the form of carbonate and hydroxide. If there is any listed as not so combined which cannot be satisfied by the other acid radicals present, the excess is probably due to some error in the analysis. I n one of the exceptions, No. 52, the percentage of silica is very high. Silica has long been known to combine with lime, even a t the temperatures found in the ordinary lime kilns, giving various silicates which do not slake with water. The high percentage of lime in other than hydroxide or carbonate form in this sample may doubtless be explained on this basis. The small amount of magnesium oxide combined as hydroxide in the fresh samples justifies to some extent the theory which has long been held in practice, that the magnesia content of a lime does not hydrate a t all. I n the older samples, however, the higher percentage of hydroxide shows that this constituent does hydrate in time, and that probably with improved methods of burning and hydration a hydrate could be produced which would be completely hidrated a t the start. I n order to determine definitely the possible effect of unhydrated magnesium oxide on a mortar or plaster. further work is necessary. At present it appears that the degree of hydration of a hydrate, in itself, means little. since in all the hydrates investigated a large percentage of the magnesia was unhydrated and yet they have all been used satisfactorily in practice. It is probable that the physical condition, rather than the mere presence, of unhydrated inaterial in commercial hydrated limes is responsible for unsoundness.
Determination of Carbon and Nitrogen on the Same Soil Sample’ By B. E. Brown SOIL
FERTILITY I N V E S I I C A T I O N S , BUREAU OF P L A N T INDUSTRY, \ v A S H I N G T O N , D.
HE usual methods for determining the carbon and nitrogen content of soils are well known. -4s a rule, the carbon is determined by the furnace method, which consists in igniting the sample in a tube through which carbon dioxide-free air or oxygen gas is passed, a long layer of copper oxide being placed near the outlet end of the tube. The so-called wet combustion method has also been tried and advocated by a number of soil chemists. The purpose of this paper is to point out to those who have nitrogen as well as carbon determinations to make on soils that after determining carbon by the wet combustion method the residue can be utilized for the determination of nitrogen. This suggestion was made by Anderson in a recent publication2 and the results given herein present similar findings, as well as results secured with oxidizing agents other than chromic acid. The removal of chlorine before proceeding with the carbon determination, as suggested by Anderson, is desirable if chlorides are present in sufficient amounts to interfere. Ames and Gaither3 employed a mixture of chromic and sulfuric acids to oxidize the carbonaceous material, the evolved carbon dioxide being absorbed in 4 per cent sodium
T
Received January 18, 1927. ‘ J . B i d . Chcm., 61, 57 (1924) 8 THIS JOURNAL, 6, 561 (1914).
c.
hydroxide solution and this solution subsequently titrated by double titration, using phenolphthalein and methyl orange, respectively, as indicators. The comparative data they presented showed a very close agreement between the “dry” and “wet” methods. The same method was employed by the writer and, in addition, the various residues, after the soils had been subjected to the action of the mixture of chromic and sulfuric acids, were used for the nitrogen determinations. It was thought that while through the action of the oxidizing mixture carbon was being converted to carbon dioxide the nitrogen in the sample would be changed completely to ammonium sulfate. If this were true, the addition of caustic soda would permit distilling off the ammonia into standard acid solution, thereby eliminating extra weighings, digeytions, etc., of a fresh sample for this purpose. hmes and Gaither state that one man can run forty-eight carbon determinations in a day, which would automatically take care of the nitrogen digestions. Experimental Work
The results reported herein were obtained on a group of ten typical loam soils. Determinations of carbon were made by the furnace and wet combustion methods, nitrogen by the Gunning method, and nitrogen in the residue from
the wet coiiihustimt I iiiiiiat,ioii. 'L'lie rcsiilts, gir.en in 'ralile I, especially tli 'or nitrogen, itre in g,wd general ztgreement,, and indicate that rrlicrc OLIO wishcs to determine carbon rind nitmgcn on the same soil sttiiiples the suggestion ollercd will prom con\-ciiicnt. l h h l e I --Total Carhon INonide and NiCro4en hy T w o Method8
Merviiric, oxide iind miiiig:ui~w perwide were also t.ried jilncc of chroinic acid, but in bot,li es the resulk iverc lower tliiiri wit11 clirumic :acid. 0xyge11 gas was passed ill
tlirnugh the inisturc iii ccrtiiiii trials, the main advantage in its use liciiig that the temperatiire coold he raised more quickly owing to iihctter regulation of tlic pressure. In a iiumbcr of inst,aiices where nitrogen deterrriiiiatioiis were made in the u,siinl way, usiiig mangniicse peroxide ill varyiiig amounts mil employing different durations of time in digestion, it >viis foiuid tiiitt digestion of tlie soils with mangaiiese peroxide nod sulfuric acid, followxl by distillation witli dkali, g a x a greater :niiouiit of nitrogen than the Gullllillg 1nethod. Summarq
The ri!snlts 0bt2~iii0dinilicrite that cz~rl~on itiid nitrugen can be deteriiiined fairly aecorately on the same soil sample by the wet combust,ioii mctlrod. Aft.er oxidizing the carbonaceous matter the residue nray be employed direct for the &termination of nitrogen in tlie iisiid way. Although t,he carbon results, exprersrxl as carbon dioxide, were lower by the wet combustion method than by the funiace method, the nitrogen was conipletely changed to ammonium sulfate without loss diiring oxidation. Mercuric oxide or manganese peroxide, when substituted for chromic acid, gave lower results. The results obtained for nitrogen, wtlen iriariganese peroxide and sulfuric acid were used, ran higher than did those obtained with the Gunning method.
Portable Laboratory Bench Units' A R T I ~ KD LITTLR, Irr., Cama~xuoa.MASS.
SPECIAL problem is presented by the use of smallA scale comniercid apparatus in the research laboratory where the type of work is varied and cannot be predicted in advancc. Such apparatus innst be readily available, easily supplied witli stemx, gas, cornprcsscd air, or electricity and, while ample working space must be provided during a series of experiments, such space in t not be wasted vhen the equipment is idle over any appre Llc period of time. In this laboratory this pruhlem lins t.mw mot, hjy the CUIIstruction of port,able bench units, each u n i t coinprisiiig it set of related equipment, arid supplied rvitli it fractionnl horsepower motor, transmission belting, gears, &., as well :as tlic necessary piping atid wiring. A special hood had been constnmted which may he used with any of the benches, and only oiic liood is required, siiice it is seldoni that two or more of tlie benches arc in use simultaneoinly on work which requires the removal of fumes, smoke, or odors. A typical unit, shown in the illustration, inr:liidcs iiiixiog nnd grinding apparatus-a sniall mixer, gas heat,ed, a paint mill, and a double pon:elain-jar ball mill. These pieces of apperatus are belted to a small countershaft, driven tlmiiigli a high-ratio reduction gear which permits the use of an iiiexpensive, higli-speed motor. The benches are coiistrricteil of l'/Anch angle iron, braced with 1-inch strap iron, They are provided with cast,ors aiid are therefore easily inoved about. The over-all dimensions arc 30 bv 42 Lv 37'/,, inches high. The use of unit benches bas uartiallv solved tlic iiiiiiuviilie problem of storage of small-scale equipment, wed For comparatively brief periods at irregular intervals. The appara-
, Received Feliiuaiy 28. 1!127.
tils is easily kept in good i:onditiiin and is always ready for immediate use, in any of the rooms of t,he laboratory. Although tlie first of the benches was made oiily a few months ago, they have already repaid their cost many times over and have been isi action on a wide variety of experimental work.
