Potash definition

But [said he] it was still necessary to learn the base of the salt. Its solution could not be precipitated either by tartaric acid in excess or by platinum chloride. Consequently it could not be potassium. I mixed another portion of a solution of the same salt with a few drops of pure potash, but without its becoming cloudy. Therefore it contained no more magnesia hence it must be a salt with soda for a base. I calculated the quantity of soda which would be necessary to form it but it always resulted in an excess of about 5 parts in 100 of the mineral analyzed. Therefore, since it seemed probable to me that the different substances might not have been well washed, Or that the analysis might not have been made with sufficient precision in other respects, I repeated it twice more with all the care possible, but always with results very little different. I obtained. Silica. 78 45, 79.85, Alumina 17 20, 17.30 Sulfate 19.50, 17.75. At last, having studied this sulfate more closely, I soon found that it contained a definite fixed alkali, whose nature had not previously been known (21). 

We are told by H. Davy that, in 1790, M. Tondi attempted to obtain the constituent elements of these earths by heating a mixture of the oxide with carbon. In some cases he obtained metallic reguli. H. Davy also pointed out that G. E. Stahl approached very nearly to the discovery of the pure alkalies, for he exposed a mixture of solid caustic potash and iron filings to a long-continued heat, and stated that in this way an intensely caustic alkali—valde causticum—is produced. The oxides were not definitely resolved into their elements until 1807, when H. Davy isolated potassium and sodium by the electrolysis of their hydroxides. 

Diphenylyl-o-arsinic acid.— This is isolated by coupling sodium arsenite with diazotised o-aminodiphenyl in alkaline solution at 50° to 00° C. in the presence of a cupric salt. Yield, about 60 per cent. It crystallises from boiling water in bristle-like needles, M.pt. 206° C. When reduced in warm concentrated hydrochloric acid by sulphur dioxide in the presence of an iodide, it yields diphenylyl-o-dichloroarsine, a heavy oil, soluble in chloroform, insoluble in water. The chloride, with alcoholic potash, yields the oxide, an amorphous substance with no definite melting-point. 

With nitrogen zirconium unites directly, but less readily than does titanium. Several nitrides have been described, but the most definite, perhaps the only, compound formed is Zr3N2. This results also when zirconium is heated in an atmosphere of ammonia, or the compounds are reduced in the presence of air. It does not burn in oxygen or chlorine, hut evolves ammonia when fused with potash. 

For over a century this definition sufficed. It was, nevertheless, unsatisfactory, being neither more nor less than a confession of ignorance and impotence. Thus it demanded that caustic potash should be regarded as an element until Davy succeeded in decomposing it by electrolysis in 1807. Similarly lime was regarded as an element and when Charles Tennant chlorinated slaked lime in 1799, the product was perforce called chloride of lime, a name that clings to it even to-day. 

Crotonic acid was discovered in croton seeds by Pelletier and Caventou by saponifying the oil, adding tartaric acid, and distilling, but was more definitely characterised by T. Schlippe. Crotonitrile C4H5N, present in crude mustard oil, yields on hydrolysis with alcoholic potash crotonic acid C4He02, and crotonitrile is formed from allyl iodide and potassium cyanide hence the acid was formulated CH2 = CH-CH2 C02H. An isomeric acid was discovered by A. Geuther in the form of an acid chloride in the products of the action of phosphorus pentachloride on acetoacetic ester. 

Although chemists had suspected for a long time that alkali earths were oxides of metals, the nature of soda and potash had not been studied up to the early 19th century. Even Lavoisier had no definite idea on this subject. He did not know what the basic constituents of soda and potash were and assumed that nitrogen could be a constituent. This confusion seems to stem from the similarity between the properties of sodium, potassium, and ammonium salts. 

Lavoisier introduced the modem definition of an element, namely that all substances that had not yet been decomposed should be accepted as elements. The table of elements given by Lavoisier (Figure 5.5) included earths such as lime and magnesia, but Lavoisier suspected that they were compounds and commented that experiment would probably soon show them to be so. He omitted the alkalis potash and soda from the list because these substances are evidently compound, although we do not know as yet the nature of the principles that enter into their composition. ... 

Berthollet emphasised that the principle is limited to neutral salts which do not form triple salts (e.g. it will not apply to alumina). Richter was aware that some salts which are saturated compounds still have an acid or alkaline reaction, and in some cases may combine with a further definite quantify of alkali or acid to form other salts. He distinguished between absolute neutrality when the acid and base united in the ratio of masses usually give a product neutral to indicators, and relative neutrality when pnly the first condition is satisfied. In relative neutrality a compound can take up an excess of one of the components, as tartar (acid potassium tartrate) can combine with a definite amount of potash or of ammonia to form a neutral salt, or sulphate of alumina can take up potash to form common alum. 

Two c.c. of oU, accurately weighed, are mixed with 10 c.c. of 2 per cent, alcoholic phenyl-hydrazine solution, and allowed to stand one hour in a glass-stoppered bottle of 50 c.c. then 20 c.c. of ded-normal hydrochloric acid and 10 c.c. of benzene are added, and the whole shaken thoroughly. The mixture is transferred to a separator, and the lower layer of 30 c.c. run through a small filter. Twenty c.c. of filtrate are titrated, after the addition of ten drops of ethyl orange 1 2000, with deci-normal caustic potash to distinct yellow coloration. By a similar blank experiment without oil the acid equivalent of the hydrazine solution is determined. From the difference between the two experiments the citral-content is calculated, each c.c. of deci-normal caustic potash corresponding to 0 0152 grm. citral. A number of analyses made in this way with mixtures of definite quantities of citral with tsrpenes were found to be well in accordance with the calculated results. 

In 1799, Joseph Proust (1754 1826) reported, "One hundred pounds of copper, dissolved in sulfuric or nitric acids and precipitated by the carbonates of soda or potash, invariably gives 180 pounds of green carbonate." This and similar observations became the basis of the law of constant composition, or the law of definite proportions ... 

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