T H E JOrR,VAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
July, 1916
for complete combustion.' T h e temperature is maintained a t 925-9 j O o C. throughout t h e combustion. T h e absorption tube2 is finally disconnected, both inlet and exit closed, allowed t o stand on t h e balance pan 1 5 min., and m~eighed.~ Little difficulty is experienced in getting duplicate determinations t o check within 0 . 0 1 per cent total carbon, equivalent t o about 0.0007 g. COZ on a 2-g. sample. A sample of acetanilide (Merck, U. S. P.no precaution taken t o purify sample) gave in duplicate determinations 0.0409 a n d 0 . 0 4 0 9 g. carbon instead of t h e theoretical quantity 0.0411 g. These determinations indicate t h a t any oxides of nitrogen formed b y t h e oxidation of organic N-compounds are sufficiently reduced, probably in the zinc tube, t o prevent absorption in t h e soda-lime bulb. T h e combustion of a previously burned sample of soil t o which was added 0 . 0 0 6 0 g. Tu', as nitrate, also failed t o show a n y increase in weight of t h e absorption bulb. I n routine work, using 2 absorption bulbs besides t h e one used as a tare in weighing, t h e time required for each determination is approximately 2 5 minutes. DEPARTME~ OF T SOILS AGRICULTURAL EXPERIMENT STATION MORGANTOWN, W E 5 T VIRGINIA
A MoDIF'CAT1oN
OF THE GAS BURETTE OF THE PARR TOTAL CARBON APPARATUS B y HOWARD LOOMIS Received March 24, 1916
While determining total and inorganic carbon in soils in this laboratory, it was soon observed t h a t many times after passing t h e mixture of air a n d carbon dioxide evolved into t h e absorption pipette the residual volume of air was less t h a n I O O cc. and could riR not be measured directly in t h e PPE-~ burette. This necessitated t h e introduction of air into t h e burette in measured volume .,.ll, ,,m sufficient t o allow the residual air in the pipette t o be measured. As originally designed no way was offered €or this b u t t o introduce air into t h e burette through t h e t u b e leading from t h e generating flask, which, after removal of t h e flask, is always filled with t h e liquid forced over t o t h e burette when t h e final portion of the air-carbon dioxide mixture is expelled from the flask and t h e tube. T h e introduction of
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this amount of liquid, containing as i t does much sediment. leaves t h e burette in a badly soiled condition after a few determinations, as well as clouding t h e liquid in t h e leveling tube, thus making correct readings difficult. T o eliminate these difficulties, a second three-way stop-cock was introduced into t h e line from the generating flask t o t h e burette, as shown in t h e accompanying sketch. By turning this cock t o open t o t h e outside air, I O O cc. or more of air can be accurately measured into the burette, then t h e residual air from t h e absorption pipette can be forced back into t h e burette as usual and its volume measured b y difference. Thus the only amount of liquid introduced into t h e burette is t h a t included between t h e t w o stopcocks, a very small amount which usually carries little sediment. AGRICULTURAL EXPERIMENT STATION BROOKINGS, SOUTH DAKOTA
APPARATUS FOR K JELDAHL DETERMINATIONS B y WYATTW. RANDALL Received June 13, 1916
I n THISJ O U R N A L 8 (1916), 5 2 1 , there is described a n apparatus whose object is t o facilitate Kjeldahl determinations. T h e flasks are closed b y means of rubber stoppers fitted with lead tubes thr-ough which t h e vapors given off are conducted t o some form of absorption vessel. To t h e present writer a n y device which permits t h e products of t h e action of hot sulfuric acid fumes upon rubber t o drip into a Kjeldahl digestion, appears on its face highly unsatisfactory, although i t must be confessed t h a t this is finding fault d priori. T h e device indicated in t h e accompanying figure has for several years been used in this laboratory with
70 d 4 ' * *
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1 Drawing t h e gas through b y suction is found preferable t o forcing i t through b y pressure, it being much easier t o prevent leakage. Any error from this source would be comparatively insignificant a s the leakage would be inward rather t h a n outward. T h e content of CO? in ordinary air is such t h a t it would require a n inward leakage of approximately 160 cc. t o cause a n increase of O . O O O ~g. in t h e weight of t h e absorption bulb. AII connections, where possible, were made of rubber stoppers, these being less liable t o develop leaks t h a n connections of rubber tubing. 2 T h e Fleming absorption bulb was found t o he very efficient, i t being possible t o increase the rate of gas flow 5 t o 8 times t h a t actually used witho u t danger of incomplete absorption of COz. 8 D u e t o t h e rather large size of the absorption bulb, some precaution is necessary in weighing t o prevent errors due t o differences in t h e amounts of moisture condensed on t h e surface of t h e bulb and t o changes in temperature and atmospheric pressure. By using a second bulb or glass bottle of approximately the same weight, containing about t h e same quantity of soda-lime, a s a tare in weighing, these errors are rendered insignificant.
great satisfaction. It calls for a little glassblowing Of a simple kind, and ought t o be easy of construction in a n y laboratory. Calcium chloride drying tubes, B , B , Of the common type are somewhat flared a t t h e wider end, until they fit more or less closely in t h e necks of t h e Kjeldahl flasks, as shown in t h e figure. T h e narrow t u b e of each is lengthened b y fusing on a piece of similar tubing, which in t u r n is bent as indicated. A glass t u b e , A , of about I O mm. bore, and of t h e proper length for t h e rack used, is provided with side tubes, c, c, fused in at the proper intervals, and with an outlet, D , dipping below the water surface in a bottle which is, in t u r n , connected with a water Pump. The bulb tubes are connected with t h e tubes C, c by means of s.hort pieces of rubber tubing; these, of course, become corroded in time and may have t o be replaced. As is evident, t h e ap-
