140 CURRENT TOPICS. [J. F. I.

foot thick. On the o ther hand, the po tash in the Bryan t well in Midland Coun ty p robab l y fills no more than a pa r t of an in terval of 2o feet covered by a single en t ry in the dri l ler 's log, and by a single sample of cut t ings . Consequent ly , though a po tash salt as good as tha t in Europe was laid down in T e x a s under p robab ly s imilar condi t ions and at abou t the same time, in associat ion wi th rock sal t and o ther saline deposits , the i m p o r t a n t points ye t to be de te rmined by the drill are whe the r the po tash deposi ts of wes t e rn T e x a s are thick enough to be mined at a profit, whe the r we have in our own country ample supplies of relatively cheap pot- ash for use in fertil izer, and whe the r these deposi ts poss ibly con- s t i tu te a g rea t po tash reserve tha t will make the Uni ted Sta tes independent of foreign impor ta t ions .

Dissociation of Hydrogen and Nitrogen by Electron Impacts. A. L. HUGHES. (Phil. Mag., May, I 9 2 I . ) - - L a n g m u i r found tha t hyd rogen is dissociated by tungs ten at a t e m p e r a t u r e above I3oo ° K. Accord ing to his calcula t ions 84,000 calories are needed to dissociate a g r am-molecu l e of the gas. F r o m this it is calcu- lated tha t the energy to dissociate one molecule is the energy g iven to one electron in fal l ing th rough a potent ia l of 3.6 volts . T h e p resen t inves t iga tor set out to see whe the r e lect rons fal l ing th rough this potent ia l in terval real ly do dissociate any molecules of hyd rogen by impact . H e finds tha t dissociat ion is not observ- able until the in terval of potent ia l reaches I3. 3 volts.

T h e hydrogen for the exper imen t was contained in a glass tube jacketed with liquid air. Along its axis was a p la t inum str ip coated wi th BaO and SrO. W h e n heated by an electric cur ren t this became a source of electrons. Nickel gauze, f i t t ing as a cyl inder into the tube. served as an anode toward which the electrons were driven f rom the platinum cathode by an applied difference of poten- tial. T h e pressure of the hydrogen ranged f rom .I mm. down- ward . T h e s t r eam of electrons was s tar ted and then readings of p ressures of the gas under expe r imen t were t aken at in tervals Of 4 minutes . T h e r e was a lways a d iminut ion of the pressure wi th the passage of time. For instance, to quote a single series of readings, the p ressure fell f rom 200 X lO -5 ram. to 8.8 of the same unit in 4o minutes . T h e absolu te change of p ressure becomes smal ler as the p ressure of the hydrogen is reduced, but the rat io of initial to final p ressure rises as the initial p ressure is made smaller . As the vo l tage be tween the electrodes was raised the ra te of p ressure change likewise rose and reached a maximum for about 14o volts, to decline somewhat for values in excess of 15o volts.

W h y does the p ressure fall while the electron s t r eam con- t inues? T h e au thor adopts the explanat ion advanced b y Lan K- mui r to accoun t for s imilar resul ts which were obta ined when dis- sociat ion was produced by high t empera tu re , viz., tha t a toms of hydrogen , resu l t ing f rom dissociation, condense progress ive ly on

July, i92I.i CURRENT TOPICS. I 4 I

the cold surface of the tube. Th i s has at least the mer i t of fur- nishing a ready elucidat ion of a phenomenon which manifes ts itself when the exper imenta l tube, in which the gas pressure has g rown smal ler owing to the electron s t ream, is heated, and then cooled. Upon hea t ing the pressure rises of course, bu t subsequent cooling to the t empe ra tu r e of the ba th does not reduce the pres- sure to its fo rmer a m o u n t when the hydrogen was at the same tempera tu re . T o cite one such exper iment , p ressure before the electrons passed in hundred-thousandths of a millimetre, 548; after their passage, ioo; af ter re -hea t ing and re-cooling, 263. I t is held that, when the t empe ra tu r e goes up, some of the a toms of gas con- densed on the cold walls get free and re -combine into molecules. W h e n the t e m p e r a t u r e again falls these remain molecules and are not condensed as they were at the same tempera tu re , while in a tomic form.

G. F. S.

Preparation of Zirconia f rom the O r e . m E . C. ROSSITER and P. I-I. SAUNDERS describe their process for the p repara t ion of zir- conia (z i rconium dioxide) f rom the ore in ]ourn. Soc. Cfiem. Ind. Trans. , I92I , xl, "20-72. The ore is finely g round in a porcela in ball mi l l ; 5 ° g r a m s of the g round ore are mixed wi th an equal weigh t of s o d m m hydrox ide ; and the mix tu re is heated in an iron crucible wi th cont inuous s t i r r ing until a g ranu la r powder is ob~ rained. T h e t empe ra tu r e is then raised to a jus t visible redness, and finally becomes approx ima te ly 6o0 ° C.; two hours are re- quired for fusion of the mixture . Whi le still hot, the contents of the crucible are t rea ted with I5oo c.c. of water . T h e insoluble por t ion is collected on a filter, and is washed wi th wa te r until free f rom alkali, then is t rea ted with hydrochlor ic acid. T h e resul t ing solut ion contains insoluble mat te r , and is evapora ted to dryness wi thou t filtration. T h e residue is ex t rac ted wi th hot w a t e r ; the solut ion is filtered, and the filtrate contains z i rconium oxychlor ide and the chlorides of cer ta in meta l s such as iron, a luminum, and manganese . T h e solution is diluted to a vo lume of I5OO c.c.; and su lphurous acid is added in am oun t s l ight ly in excess of that re- quired to reduce the iron presen t in the solut ion comple te ly to the ferrous state. Then the solut ion is heated to boiling, and normal sulphuric acid is added in a m o u n t theoret ical ly required to re- place the chlorine content of the oxychloride. All of the zirco- nium presen t in the solution precipi ta tes as a basic sulphafe. For quant i t a t ive results, 7 c.c. of a sa tu ra ted solut ion of su lphurous acid and 2 c.c. of a normal solution of sulphuric acid should be used for each o.2 g r a m of z i rconium dioxide ; and the solut ion con- ta in ing the z i rconium should be so dilute tha t it has a vo lume o f at least I5o c.c. for each 2 c.c. of normal sulphuric acid to be added. I f the prec ip i ta te be washed five t imes by decanta t ion in a glass cyl inder of 6 litres capaci ty, the soluble impuri t ies are