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XIV.—On the preparation of certain chlorates, particularly of chlorate of potash

 

作者: F. Crace-Calvert,  

 

期刊: Quarterly Journal of the Chemical Society of London  (RSC Available online 1851)
卷期: Volume 3, issue 2  

页码: 106-111

 

ISSN:1743-6893

 

年代: 1851

 

DOI:10.1039/QJ8510300106

 

出版商: RSC

 

数据来源: RSC

 

摘要:

106 PROFES/OR CALVERT ON THE PREPARATION XIV.-On the Preparation of certain Chlorates particularly of Chlarate of Potash. Owing to the importance which chlorate of potash has acquired within the last two or three years in our manufacturing districts due principally ta its application as an oxidizing agent in steam colours to raise their intensity and increase their beauty and also in conse-quence of the high price which commercial potashes have attained during the last two years without any prospect of becoming cheaper I was indlrced a few months back to try if any other chlo- rate could be introduced as a substitute for that of potash; and also whether a cheaper method could not be devised for manufacturing that important commercial product of which the useful application as an Oxidizing agent is greatly impeded by its high price.For it is well known that potashes have averaged for the last two years from &2 to BEa. 5s. a hundred weight which quantity does not contain above 39 to 41 per cent of potash the remaining amount of alkali often quoted to exist in the salts being soda. It may be stated that in all the potashes which I have analysed I have uniformly found from 10 to 12 per cent of Bods. My attention was first directed to the preparation of the chlorate of lime which I produced by passing a current of chlorine gas into a thick milk of lime nearly boiling. It appeared after several expe- riments that heat had great influence in assisting the oxydation of the chlorine. For whilst at ordinary temperatures I could only obtain hypochlorite of lime at about 200' or 212' F.little or no hypophlorite was formed but a large amount of chlorate of lime. It will be seen immediately that it was the observation of the remarkable influence of a temperature of about 212' F. to increase the degree of acidification of chlorine which led me to the discovery of a new method of preparing chlorate of potash. I tried for some time to find a mode of separating chlorate of lime from chloride of calcium. But the chlorate is not to be separated with facility from the highly deliquescent chloride of calcium. A curious chemical reaction was observed to take place several times during the numerous trials which were made on this point. It was that large amounts of pure oxygen were often given off; OF CHLORATE OF POTASH.107 and on every recurrence of such an action no eblorate was pro-duced. I next directed my attention to the preparation of the chlorate of baryta the commercial manufacture of which would haye been greatly enhanced by the recent opening of an extensive mine of car-bonate of baryta at Pride Hill in Wales near Shrewsbury. The mineral referred to yields on an average 90 per cent of pure carbonate in fqct its high degree of purity has caused its success- ful application at the potteries and also in the finishing of calicoes as a substitute for carbonate of lead in the glazisg of cgrds &c. I at first followed the process described in chemical works namely the passing of a current of chlorine gas through water holding car- bonate of baryta in suspension Iqstead of forming chlorate I only produced a hypochlorite; but when a heat of from 200 to 212O F.was communicated to a thick milk of carbonate of baryta one of the neatest chemical reactions took place for the whale mass was transformed into chlorate of baryta and chloride of barium. It appeared to me at the time that a cheap substitute for chlorate of potash was thus obtained. But I was deceived; as it was found impossible to separate in a satisfactory manner the chlorate of baryta from the chloride of barium even by seven or eight consecutive crys- tallizations from water. Though certainly the chlorate was becoming gradually purer still it was impossible to free that salt completely from chloride of barium.Although this coincidence in the solu-bility of these two salts had been remarked by Chenevix still a% in most works the chlorate of baryta is stated to be employed to prepare chloric acid I persevered but regret to say in vain. I even tried to separate these two salts by treating them with rectified spirits and wood-naptha or the hydrate of oxide of methyl but without success. I next directed my efforts to discover a cheaper method than those hitherto known of preparing the chlorate of potash. It is necessary here to mention that the chloratr of potash is not now generally manufactured by passing chlorine into a concentrated solution of carbonate of potash but that the useful process recom- mended by Professor Graham namely of carrying a current of chlo-rine through a mixture of sulphate of potash and lime has been generally adopted and has given satisfactory results.I placed myself in the best circumstances for ascertaining the relation of this process to the one hereafter described. One equiva- lent or 97 parts of sulphate of potash dissolved in a sufficient amount of water and mixed with six equivalents of lime or 168 PROFESSOR CALVERT ON THE PREPARATION parts was submitted to a current of chlorine at 212O I?. Although chlorate of potash was formed in this experiment yet its quantity was inferior to the theoretical amount naniely 122.5 parts. From this and other experiments and also from information which I have obtained I find that commercially 122.5 parts of chlorate of potash are never produced from 97 parts of sulphate of potash.No doubt this result is due to the formation of a certain amount of chloride of potassium in addition to the imperfect decomposition of the sulphate of potash by the lime. A mixture of chloride of potassium with lime was also submitted to experiment but yielded no satisfactory results. It was several months after my researches were completed that I learnt from Professor Graham himself that he had published in the lCTransactions of the Chemical Society,J’ (Vol. I. p. 5) a short notice on the production of the chlorate of potash by means of a mixture of carbonate of potash and lime. Still this chemist has not inquired into the precise bearing of his interesting observation as to the best mode of conducting the process commercially and the amount of chlorate produced.I was led by a series of consecutivc trials to examine what would take place by passing chlorine gas at ordinary temperatures through a solution of caustic potash containing caustic lime in suspension. Under these circumstances I only produced the hypochlorites of potash and lime and the chlorides of potassium and calcium; but if the chemical action was assisted by heat chlorate of potash was formed in large amount instead of hypochlorite. It is certainly interesting to see in this series of experiments how a comparatively small increase of temperature (from 60° to 180O) modifies chemical action and assists the fixation of an additional amount of oxygen by the chlorine.Having been successful so far niy attention was next directed to the best means of producing by this method the largest amount of chlorate of potash an object which I arrived at by examining thc influence of solutions of caustic potash more or less concentrated upon the quantity of salt produced. For my first experiment a solution of caustic potash of specific gravity 1.040 at 60°F. was taken containing 34 grains of real potash in 1000 fluid grains of liquid. In order aIso to act always on the same proportion of potash a constant bulk of fluid was taken nhich contained exactly 100 grains of oxide of potassium. In this case therefore 3000 fluid grains were made use of containing 102 grains of potash.I then took 6 equivalents of good quick lime or OF CIILORA'PE OF POTASH 109 358 grains which after being slaked mere added. The mixture being heated to about ZOOf) F. a rapid current of chlorine was passed through as long as the gas was absorbed. The whole was thrown on a filter and the small deposit washed with boiling water. The liquor in cooling yielded a fair amount of chlorate which was slightly increased by the concentration of the mother-liquor. The quantity was 130 grains of chlorate or 3 times as much as potash alone would have given. A second experiment was made with a solution of caustic potash of specific gravity 1.050 and containing 40 grains of potash in 1000 fluid grains; consequently 2778 grains of this caustic solution were taken and contained 100 grains of oxide of potassium.After being mixed with the required proportion of slaked lime they were submitted to the operation above described and gave 140 grains of chlorate of potash exclusive of a small amount of that salt left in the mother-liquor. As an increase in the quantity of caustic potash for a given bulk of fluid appeared therefore favourable a third trial was now made with a solution of specific gravity 1.070 containing 58.75 grains of oxide of potassium in 1000 fluid grains; or 1750 grains contained 102 grains of oxide of potassium. In this trial 158 grains of chlorate were produced. Such details on the action of chlorine on solution of caustic potash at different strengths may be excused as they afford an interesting illustration of the modifications which chemical actions may undergo in consequence of the influence of small changes either in the mode of operating or in the medium in which the reactions takes place The results perfectly corroborate the facts which I formerly observed respecting the action of ammonia on the nitrate of lead as well as the remarks vhich I then made on the formation of the salts resulting from the action of these two compounds.It was necessary to proceed very cautiously with this series of ex- periments as I had remarked that if a particular strength in the solution of caustic potash was exceeded I then produced chloride of potassium and less chlorate. Another serious impediment was also created by the liquor becoming so thick by the amount of lime re-quired for a given weight of potash that the free passage of chlorine gas was prevented.In a fourth experiment I took a solution of caustic potash of specific gravity 1.090 at 60° F. A quantity of liquor containing 100 grains of potash gave 172grains of chlorate. In a fifth trial a liquor of specific gravity 1.099 being used 100 grains of potash gave 185 grains of chlorate besides some left in 110 PROFESSOR CALVBRT ON CHLORATE OF POTASH. the mother-liquor. This last quantity already exceeded more than faur times that which potash alone would have furnished. In a sixth experiment an enormous amount of chlorate was pro- duced amounting as it will be seen to nearly the theoretical propor-tioh namely 260 parts of chlorate for 100 parts of potash ; and I have no doubt that in manufactures the amount produced would be still nearer as the portion left in the mother-liquor would be com- paratively less.A solution was finally employed of caustic potash of specific gravity 1.110 or containing 105333 per cent of real potash ; conse-quently the quantity of fluid operated upon 1000 fluid grains con-tained 102-83 grains of oxide of potassium. To this liquid was added 358 grains of quick lime previously slaked. The whole being slightly heated a rapid current of chlorine gas was passed through the temperature rising very fast to 180° F. owing to the intensity of the chemical action. The operation was considered complete when the liquid refused to absorb any more gas; the whole was then eva- porated nearly to dryness the residue dissolved in boiling water and the liquor filtered.After washing the slight deposit left on the filter the whole of the liquors were evaporated for crystallization. The amount of chlorate of potash obtained in this experiment was equal to 220 grains with some salt still left in the mother-liquors. The last no doubt amounted to nearly 20 grains owing to the rather large bulk of mother-liquors which were reserved so as to prevent the chlorate from being soiled with chloride of potassium. It is certainly remarkable that there should be a determinate spe- cific gravity where the chemical reaction is brought to bear to its fullest extent or where in other words the whole of the potash is transformed into chlorate while in solutions of greater or less speci- fic gravity a smaller quantity of chlorate is produced with a corres-ponding increase of chloride of potassium.This chemical reaction is rendered still more worthy of notice by the influence of the above fact in modifying the action of chlorine relatively to its affinity for potassium or calcium. Thus in a liquor of specific gravity 1.110 we find that calcium takes precedence of potassium in combining with chlorine and preserves the latter metal almost entirely from the action of chlorine ; while the oxygen disengaged from the calcium applies itself to the chlorine to transform the latter into chloric acid which neutralizes the potash only. This so far as I am aware is the only example which chemistry affords where in the presence of two bases the chlorine applies itself almost entirely to one of the metals whilst oxygen attaches itself to the chlorine converting it CAPTAIN REYNOLDS ON PROPYLENE into an acid which neutralizes exclusively the second base namely the patash.The commercial advantages of the above process over the old one will be easily conceived when we reflect that in the latter 100 parts of oxide of potassium yielded only 43 parts of chlorate whilst treated by the method here recommended 100 parts of the same oxide give nearly 260 parts of chlorate of potash. The chlorate may be produced by the new process at about seven- pence per pound and might therefore be supplied on terms which are greatly below the present market price. Before concluding I have much pleasure in acknowledging the valuable assistance which I have received in this inquiry from one of my former pupils Mr. Charles O’Niel of thi- 3 town.

 

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