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mean velocity head is needed; a n d t o o b t a i n a correct m e a n velocity head i t is necessary t o average t h e square roots of all t h e velocity h e a d readings t a k e n , t h r o u g h o u t t h e cross-sectional a r e a of t h e pipe, a n d t h e n t o s q u a r e t h e average. T h e r e is a t present no royal road t o obtaining acc u r a t e velocity measurements b y means of t h e pitot t u b e . Investigators, t o o b t a i n accurate results, m u s t h a v e recourse t o t h e painstaking methods a d o p t e d b y Rowse. We are told t h a t , for a 12-inch pipe, results within 2 per cent of correct m a y be obtained b y using 0.8 of t h e velocity h e a d i n feet of gas a t t h e center of t h e pipe. Lacking similar factors for pipes of other sizes, velocities m u s t be calculated from readings t a k e n a t ntimerous points in t h e cross-sectional area of t h e pipe. I n recapitulation, it m a y be observed t h a t : I--As a result of t h e work of Rowse, engineers m a y now select a t y p e of p i t o t t u b e which m a y be used, under certain conditions, with confidence. 11-Further investigation needed, t o render t h e p i t o t t u b e more generally available a s a means of measuring gas velocities, includes: I-A means of determining accurately t h e velocity of gases i n pipes whose length is less t h a n 20 t i m e s t h e diameter. a-The establishment of definite relations between t h e velocity h e a d a t t h e center of a pipe, a n d t h e m e a n velocity head, f o r pipes of various sizes a n d shapes. NOTE-I a m indebted t o t h e a u t h o r of t h e original paper which constitutes t h e basis for t h i s one-Mr. W. C . Rowse-for his courtesy in reading t h i s m a n u script, a n d for valuable suggestions offered b y h i m a n d a d o p t e d herein. COPPERHILL, TENNESSEE
THE NON-UNIFORMITY OF DRYING OVEN TEMPERATURES By LORIN H. BAILEY Received April 13, 1914
While testing t h e accuracy of t h e h e a t control of a new electric drying oven, i t was observed t h a t t h e r e
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I n t h e above tests only those thermometers were used which h a d been standardized b y t h e Bureau of S t a n d a r d s . W i t h ovens having glass doors t h e t h e r mometers were placed on t h e shelves a n d t h e temperatures read b y making t h e observations through t h e glass i n t h e door without opening t h e oven. W i t h t h e o t h e r ovens t h e following scheme was a d o p t e d : Six 50 cc. Erlenmeyer flasks were filled with clean, d r y s a n d , stoppered, a n d t h r o u g h t h e stoppers t h e thermometers were inserted so t h a t t h e bulbs were held i n t h e middle of t h e flasks. These flasks with their thermometers were t h e n placed i n t h e various positions i n t h e ovens a n d after having remained t h e r e long enough t o come t o equilibrium t h e y were removed a n d t h e thermometers read a s quickly a s possible. While t h i s m e t h o d is not absolutely accurate, i t is sufficiently so t o indicate whether or n o t t h e r e is a n y great variation i n t e m p e r a t u r e . After testing these various drying ovens t h e writer's a t t e n t i o n was called t o a n article t o R . G. Grimwoodl o n t h e "Analysis of Crude Glycerine b y T h e International S t a n d a r d Methods, 191 I . " I n t h i s article t h e a u t h o r mentions difficulty when using a drying oven which complies with t h e International S t a n d a r d Methods specifications a n d which shows a m a x i m u m variation of 16" C. on one shelf a n d between t h e t w o shelves a maximum variation of 4 j o C. H e t h e n describes a special electric drying oven which h a s proved satisfactory for drying glycerin. This oven showed a m a x i m u m variation of z . z o C . from 160' C., t h e t e m p e r a t u r e desired. T h e results shoa-n b y M r . Grimwood are very much b e t t e r t h a n t h e writer was able t o obtain with a n y oven n o t surrounded b y boiling water a n d s t e a m . T h e results i n t h e above table show t h a t elaborately designed a n d expensive ovens are no more reliable t h a n t h e most simple a n d inexpensive ones. Of t h e ovens tested. only those surrounded b y boiling mater a n d s t e a m are capable of maintaining even approximately uniform t e m p e r a t u r e s . I wish t o t h a n k D r . J. A. LeClerc for his interest
Reading of Maximum range of temperature on Maximum thermometer . variation Approximate inserted through ___* top of oven top shelf lower shelf on both shelves inside dimensions in. O C OC O C OC No. Kind of oven 107 99-114 90-108 24 12 X 12 X 14 1 Electrically heated and controlled.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 89-100 88-103 15 12 X 13 X 18 2 Electrically heated and controlled. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 94-104 89-102 15 9 x 9 x 1 5 3 Electrically heated and controlled.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 8892 92-102 14 11 X 12 X 16 4 Gas heated porcelain lined., . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 94- 96 105-118 24 8 X 10 X 11 ... 5 Gas heated air jacketed.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 9699 9598 4 13 X 15 X 15 6 Gas heated constant level water and steam jacketed., . . . . . . . . . . . . 100 101-101 101-102 2 15 X 8 in. diam. 7 Steam jacketed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 100-100 100-100 0 15 X 8 in. diam. 8 Gas heated constant level water and steam jacketed vacuum oven. .
was a wide range of t e m p e r a t u r e i n different p a r t s of t h e oven, not only between different shelves b u t also between different positions on t h e . s a m e shelf. Ordinarily t h e t e m p e r a t u r e recorded o n t h e t h e r m o m e t e r inserted t h r o u g h t h e t o p of a n oven is t a k e n a s t h e t e m p e r a t u r e a t which t h e drying is m a d e , b u t i t was seen t h a t such could n o t be done with t h i s particular oven. Following t h i s observation a n u m b e r of differe n t t y p e s of drying ovens were tested a s t o their uniformity of t e m p e r a t u r e s t h r o u g h o u t t h e drying c h a m bers. T h e variations i n t e m p e r a t u r e a r e shown i n t h e accompanying table.
a n d suggestions i n connection with t h e testing of these various ovens a n d t h e writing of t h i s report. LABORATORY OF PLANT CHEMISTRY, BUREAU OF CHEMISTRY u. s. DEPARTMENT O F .kGRICULTURE, m ' A S H I N G T O N
A MANOSTAT FOR USE IN GAS ANALYSIS By HARVEYN. GILBERT Received April 14, 1914.
I n t h e combustion of gases confined over mercury i n a combustion pipette, more or less difficulty is always experienced b y t h e operator i n avoiding a difference of pressure d u e t o t h e difference of level between t h a t 1
J. SOC.Chem. I n d . , 38, 22.
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of t h e mercury in t h e pipette a n d t h a t in t h e level B y moving t h e point of support of t h e spring on bulb. This is ordinarily accomplished b y resting t h e lever a r m i t can be so adjusted t h a t t h e vertical t h e level bulb on a pile of blocks which can b e removed distance through which t h e p a n moves, when t h e spring or a d d e d t o as m a y be necessary. B u t these blocks is deflected, is just equal t o t h e height of t h e column are inconvenient a n d usually t h e y are thick enough of mercury which has left t h e pipette in order t o produce t o cause considerable difference in t h e level of the this deflection. mercury. Furthermore, t h e a b r u p t changing of t h e T h e principle is rendered clearer if one considers pressure m a y cause leakage in t h e rubber connections t h e level bottle suspended directly on a spring. A a n d m a y lead t o explosions in cases where t h e rapid unit weight of mercury produces a n elongation of lowering of t h e pressure i n t h e pipette during t h e prog- t h e spring which is just equal t o t h e height of this ress of a combustion causes t h e gas t o enter t h e pipette ’ a m o u n t of mercury when i t is confined in t h e pipette. too rapidly. T h u s t h e level of t h e mercury is automatically k e p t T h e following a p p a r a t u s is designed t o overcome constant during t h e entire combustion. these difficulties b y maintaining a constant level of T h e above form of t h e a p p a r a t u s was designed in t h e mercury during t h e combustion, t h u s insuring order t o make i t possible t o use different sizes of level constant pressure. T h e device bottles a n d pipettes, a n d also t o make i t easy t o reshown in t h e accompany- place t h e spring b y others of different strengths. ing figure consists of a metal Economy of space was another reason for adopting base a n d a n upright which this form. While this form is not mathematically supports parallel lever arms. exact, a s is t h e case of t h e freely suspended spring, At t h e ends of these a r m s is i t maintains a pressure which is constant for all pracattached a p a n which moves tical purposes. T h e a p p a r a t u s can also be made t o vertically, b u t always remains maintain a constant pressure either above or below in a horizontal position. T h e t h a t of t h e atmosphere, b y adjusting t h e spring as level bottle is connected as described before. usual with t h e combustion T h e principle is capable of other applications t o pipette b y means of rubber a p p a r a t u s for handling a n d measuring gases. t u b i n g a n d i t is placed upon T h e a p p a r a t u s is manufactured b y Greiner a n d t h e p a n . A coil spring is sus- Friedrichs, Stutzerbach in Thuringen, Germany, a n d pended from t h e upper p a r t of t h e framework a n d is known a s t h e “Gilbert Manostat.” is attached t o a n adjustable point on t h e lever a r m . CORNELL UNIVERSITY,I T H A C A , h’Ew Y O R g
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THE EXCESSIVE QUANTITIES OF NITRATES IN CERTAIN COLORADO SOILS By W x . P. HEADDEN Received April 21, 1914
The Colorado Experiment Station has issued, up to the present time, eight publications1 pertaining to the occurrence and origin of excessive quantities of nitrates in certain soils. These remarkable occurrences were first definitely recognized about r g o j . The difficulty of accounting for the nitrogen necessary to form these nitrates presented itself from the very first, but no other theory than the fixation of atmospheric nitrogen seemed available and adequate. The above mentioned publications report the occurrence and distribution of the nitrates and their effects upon vegetation, particularly upon apple trees, but also upon the quality of sugar beets. The source of these nitrates is sought in the activity of the bacterial flora of the soils. This view is urged on the ground that there is no known source from which the nitrates may be derived ready formed. The distribution of the nitrates is such as to preclude their derivation from any system of rocks, and they are so widely distributed that some generally prevailing condition must be operative in their production. The direct evidence adduced consists of a series of consistent facts which support this contention; i. e . , these soils have been shown, by direct experiment, to fix nitrogen in a marked degree, and also to change it into nitric acid (nitrates) very much more energetically than do eastern, southern and foreign soils in general. The fixation is attributed to the azotobacter which are found t o
* Bulls. 166, 160, 178, 183 and 186, b y Wm. P. Headden; 179 and 193, by Walter G. Sacliett; 184, b y Walter G . Sackett and W. W. Robbins.
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occur in these soils in great abundance, and whose characteristic pigment constitutes the first most striking character of these niter-areas. The appearance of this color has been recognized very generally by the orchardists and ranchmen as the beginning of serious trouble. It is related throughout these publications that complaints were made that the land turned brown and then the trees died, or that nothing would grow. The very first occurrences examined had been mistaken as exudations of oil. The surface of the ground was black and glistening. The areas involved were small and nearly circular. An analysis of the surface soil showed the presence of 13.4per cent of water-soluble material, of which nearly 42.0 per cent consisted of nitrates. These were largely the calcic and magnesic salts. There was a number of such brown areas, mostly smaller than the one referred to, in this locality. That such areas should be destitute of vegetation would seem a natural and even necessary result of the presence of such quantities of nitrates, in this case j.6 per cent of the air-dried soil. Other and larger areas were observed, which were either devoid of vegetation, or on which the vegetation was suffering without the presence of any evident cause. Examination of such cases showed the presence of unduly large amounts of nitrates. These facts enlarged the question from one of scientific curiosity t o one of very great agricultural importance. Individual orchardists had, in the meantime, taken cognizance of the fact that this was a serious trouble and that there was an intimate connection between the turning brown of the soil and the death of the vegetation, whether orchard trees, alfalfa or vegetables. Complaints of “brown-spots on which nothing will grow” became quite numerous and pointed the way to new localities for these
