Plate sulphate

Hence sulphuric acid is used up and insoluble lead(II) sulphate deposited on both plates. This process maintains a potential difference between the two plates of about 2 V. If now a larger potential difference than this is applied externally to the cell (making the positive plate the anode) then the above overall reaction is reversed, so that lead dioxide is deposited on the anode, lead is deposited on the cathode, and sulphuric acid is re-formed. Hence in the electrolyte, we have ... 

This is used extensively for qualitative analysis, for it is a rapid process and requires simple apparatus. The adsorbent is usually a layer, about 0 23 mni. thick, of silica gel or alumina, with an inactive binder, e.g. calcium sulphate, to increase the strength of the layer.. A. i i slurry of the absorbent and methanol is commonly coated on glass plates (5 20 cm. or 20 x 20 cm.), but microscope... 

Phthalide. In a 1 litre bolt-head flask stir 90 g. of a high quality zinc powder to a thick paste with a solution of 0 5 g. of crystallised copper sulphate in 20 ml. of water (this serves to activate the zinc), and then add 165 ml. of 20 per cent, sodium hydroxide solution. Cool the flask in an ice bath to 5°, stir the contents mechanically, and add 73-5 g. of phthalimide in small portions at such a rate that the temperature does not rise above 8° (about 30 minutes are required for the addition). Continue the stirring for half an hour, dilute with 200 ml. of water, warm on a water bath imtil the evolution of ammonia ceases (about 3 hours), and concentrate to a volume of about 200 ml. by distillation vmder reduced pressure (tig. 11,37, 1). Filter, and render the flltrate acid to Congo red paper with concentrated hydrochloric acid (about 75 ml. are required). Much of the phthalide separates as an oil, but, in order to complete the lactonisation of the hydroxymethylbenzoic acid, boil for an hour transfer while hot to a beaker. The oil solidifles on cooling to a hard red-brown cake. Leave overnight in an ice chest or refrigerator, and than filter at the pump. The crude phthalide contains much sodium chloride. RecrystaUise it in 10 g. portions from 750 ml. of water use the mother liquor from the first crop for the recrystaUisation of the subsequent portion. Filter each portion while hot, cool in ice below 5°, filter and wash with small quantities of ice-cold water. Dry in the air upon filter paper. The yield of phthalide (transparent plates), m.p. 72-73°, is 47 g. 

Methylation of the Alkaloids. When cephaeline is treated with methyl sulphate or sodium methyl sulphate under various condition, there is formed in addition to emetine (which was first shown to be the methyl ether of cephaeline and partially synthesised in this way by Carr and Pyman in 1913), more or less N-mcthylcephaeline (wedge-shaped plates, m.p. 194 5°), and N-methylemetine. The latter is also obtained by direct methylation of emetine it is amorphous, [a]n — 52-6° (CHCI3), but yields a hydrobromide, C33H42O4N2.2HBr. 3H2O, m.p. 210-30°, [ajp + 5-6° (H2O). 

Pilosine, CjgHjgOgNj, obtained by Pyman (and almost simultaneously by L ger and Roques, who named it carpidine) from mother liquors remaining after the isolation of pilocarpine and isopilocarpine from the total alkaloids of P. mi.crophyllus, crystallises from alcohol in large colourless plates, m.p. 187°, [a]n + 39-9° (EtOH), lasvorotatory in alkaline solution. The salts do not crystallise readily the sulphate,. H SO, forms clusters of plates, m.p. 194-5°, fajD + 21° (HgO) the acid tartrate, B. H2C4HiOg, has m.p. 135-6°, [a]n + 24-2°, and the aurichloride, B. HAuCb, m.p. 143-4°. 

HjO) and Bj. H2SO4.4HjO, m.p. 203-4°, [a] ° + 120° the acid sulphate, B. HjSO, occurs in yellow prismatic needles, m.p. 246-8° (corr., dec.), [a]n + 113-1° (HjO) the hydrochloride forms yellow, pentagonal plates, m.p. 286° (corr., dec.), and shows a purple fluorescence in solution in alcohol the picrate separates from alcohol in rosettes of reddish-orange needles, m.p. 194-5° (cort.). Dilute solutions of the salts are yellow and show a marked blue fluorescence. Alstonine behaves as a monoacidic base, contains one methoxyl but no methylimino group, and, unlike echitamine, does not give indole colour reactions. 

Before filtering an inflammable liquid such as alcohol the flame must be removed. The potassium ethyl sulphate is dried on a plate of unglazed earthenw are or on a thin pad consisting of three or four sheets of filter paper, with another sheet ovdr the ciystals to keep out the dust. On concentrating the mother liquors on the water-bath, a further quantity of ciystals may be obtained. Yield 35—40 giams. The following equations express the chemical reactions which occur ... 

The fi-compound is dissolved in 50 c c. pure dry ether, and dry hydiogen chloride is passed in with constant shaking to prevent the delivery tube from becoming blocked. Colourless crystals of the hydrochloride of the /3-o ime separate and aie filtered and washed with dry ether and then placed in a separating funnel and covered with a layer of ether. A. concentrated solution of sodium carbonate is gradually added with constant shaking until no further effervescence is observed. Sodium chloride is precipitated and the /3-oxime dissolves in the ether. The ether extract is sepaiated, dehydrated over sodium sulphate, and the ether remoi ed as rapidly as possible at the ordinary temperature by evaporation in vacuo. The residue crystallises, and when pressed on a porous plate leaves a mass of small silky needles, m. p. 126—130A It may be re-... 

Naphthyl methyl ether.—Dissolve 3-6grams(3-naphthnl in I3 5 c.c. 10 per cent, caustic soda solution, add 3 c.c. meth l sulphate, warm the liquid gently and shake vigorously. In. i short time the naphthyl methyl ether separates as a solid mass. The product is heated for ten minutes on the water-bath, a little water is added, and the naphthyl ether filtered and washed with water. It is crystallised from alcohol and deposits in lustrous plates m. p. 70—72°. The yield is theoretical. It may be used for analysis by Zeisel s method. 

Salt solutions When a zinc sheet is immersed in a solution of a salt, such as potassium chloride or potassium sulphate, corrosion usually starts at a number of points on the surface of the metal, probably where there are defects or impurities present. From these it spreads downwards in streams, if the plate is vertical. Corrosion will start at a scratch or abrasion made on the surface but it is observed that it does not necessarily occur at all such places. In the case of potassium chloride (or sodium chloride) the corrosion spreads downwards and outwards to cover a parabolic area. Evans explains this in terms of the dissolution of the protective layer of zinc oxide by zinc chloride to form a basic zinc chloride which remains in solution. 

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