Crystalline deposits

Add in turn benzyl chloride (8 3 g., 8 o ml.) and powdered thiourea (5 gm.) to 10 ml. of 95% ethanol in a 100 ml. flask fitted with a reflux condenser. Warm the mixture on the water-bath with gentle shaking until the reaction occurs and the effervescence subsides then boil the mixture under reflux for 30 minutes. Cool the clear solution in ice-water, filter off the crystalline deposit of the benzylthiouronium chloride at the pump, wash it with ice-cold ethyl acetate, and dry in a desiccator. Yield, 11-12 g., m.p. 170-174°. The white product is sufficiently pure for use as a reagent. It is very soluble in cold water and ethanol, but can be recrystallised by adding ethanol dropwise to a boiling suspension in ethyl acetate or acetone until a clear solution is just obtained, and then rapidly cooling. 

Solvent for Electrolytic Reactions. Dimethyl sulfoxide has been widely used as a solvent for polarographic studies and a more negative cathode potential can be used in it than in water. In DMSO, cations can be successfully reduced to metals that react with water. Thus, the following metals have been electrodeposited from their salts in DMSO cerium, actinides, iron, nickel, cobalt, and manganese as amorphous deposits zinc, cadmium, tin, and bismuth as crystalline deposits and chromium, silver, lead, copper, and titanium (96—103). Generally, no metal less noble than zinc can be deposited from DMSO. 

The lDcii70in and nltiic acid are heated on the water-bath with an. >ir condenser, the flask being occasionally shaken. Nitrous fumes arc evolved, and the crystals of benzoin are converted into a yellow oil, which, after two hours heating, is free from un-(hanged benzoin. The contents of the flask are now poured into water, and the yellow crystalline deposit separated by filtration, washed with water, and recrystallised fiom alcohol. Yield, 10—12 grams. 

As an inhibitor of xanthine oxidase, allopurinol also markedly decreases oxidation of both hypoxanthine and xanthine itself to the sole source of uric acid (19) in man. This metabolic block thus removes the source of uric acid that in gout causes the painful crystalline deposits in the joints. It is of interest that allopurinol itself is oxidized to the somewhat less effective drug, oxypurinol (21), by xanthine oxidase. 

Two grams of the oU are saponified the portion insoluble in water separated by shaking with ether, and the aqueous solution neutralised with acetic acid. The solution is dUuted to 50 c.c. and 10 c.c. of cold saturated solution of barium chloride added. It is then warmed for two hours on a water-bath and allowed to cool. If a crystalline deposit is formed, the oil is to be considered adulterated, as the acids contained in normal lavender oil, acetic and butyric acids, give soluble barium salts. It is evident that this test will only detect those acids whose barium salts are insoluble. A more comprehensive test is therefore needed, as several other esters have since been employed for adulteration purposes. Glycerin acetate, prepared by the acetylation of glycerine, was first de-... 

One gram of 6,7-dihydro-5H-dibenz[c,e] azepine hydrochloride was dissolved in water, made alkaline with concentrated ammonia, and the resultant base extracted twice with benzene. The benzene layers were combined, dried with anhydrous potassium carbonate, and mixed with 0.261 g of allyl bromide at 25°-30°C. The reaction solution became turbid within a few minutes and showed a considerable crystalline deposit after standing 3 A days. The mixture was warmed VA hours on the steam bath in a loosely-stoppered flask, then cooled and filtered. The filtrate was washed twice with water and the benzene layer evaporated at diminished pressure. The liquid residue was dissolved in alcohol, shaken with charcoal and filtered. Addition to the filtrate of 0.3 gram of 85% phosphoric acid in alcohol gave a clear solution which, when seeded and rubbed, yielded 6-allyl-6,7-dihydro-5H-dlbenz[c,e] azepine phosphate, MP about 211°-215°C with decomposition. 

The electrolytic deposit should be salmon-pink in colour, silky in texture, and adherent. If it is dark, the presence of foreign elements and/or oxidation is indicated. Spongy or coarsely crystalline deposits are likely to yield high results they arise from the use of too high current densities or improper acidity and absence of nitrate ion. 

Other university experiments have found that under certain scaling conditions, with the right combination of magnetism, temperature, acidity, and water flow rate, the rate of scaling can be halved and that the scale so formed is not in the form of adherent crystalline deposits, but rather a sludge or powder that is fairly easily removed. 

Crystalline deposits are obtained with Reaction (2) in the temperature range of 350-400°C at low pressure (< 1 Torr).P9] At still lower temperature (< 330°C) and moderate pressure (20-50 Torr), an amorphous germanium deposit is obtained. With Reaction (2), germanium is obtained by plasma CVD at 450°C and by laser CVD at 340°C.[31][32]... 

Based on voltammetry and solid-state characterization results. Pettier and Maurin [175] defined the electrochemical conditions leading to the formation of smooth crystalline deposits of CuInSe2 and also of the related binary compounds... 

Different ways of the structural classification of deposits exist. In one system, the following structures are distinguished arbitrarily (1) fine-crystalline deposits lacking orientation, (2) coarse-crystalline deposits poorly oriented, (3) compact textured deposits oriented in field direction (prismatic deposits), and (4) isolated crystals with a predominant orientation in the field direction (friable deposits, dendrites). The structure of metal deposits depends on a large number of factors solution composition, the impurities present in the solntion, the current density, surface pretreatment, and so on. 

A very general rnle can be formnlated In metal deposition, higher activation polarization will favor the formation of fine-crystalline, compact deposits. Friable, coarse-crystalline deposits are formed in the deposition of poorly polarizable metals in solutions of simple salts, bnt relatively compact, fine-crystalline deposits are formed in the deposition of metals having high polarizability. A strong increase in polarization, and hence the formation of fine-crystalline deposits, will resnlt when... 

The formation of new nuclei and of a fine-crystalline deposit will also be promoted when a high concentration of the metal ions undergoing discharge is maintained in the solution layer next to the electrode. Therefore, concentration polarization will have effects opposite those of activation polarization. Rather highly concentrated electrolyte solutions, vigorous stirring, and other means are employed to reduce concentration polarization. Sometimes, special electrolysis modes are employed for the same purposes currents that are intermittent, reversed (i.e., with periodic inverted, anodic pulses), or asymmetric (an ac component superimposed on the dc). 

Flower shaped crystalline deposit on the surface of the solid non-crystalline mass of platinum sulphide was probably due to the precipitation of elemental sulphur, which deposited as a floral growth on the non-crystalline platinum sulphide precipitate. Ultrasonic irradiation seemed to have broken tender sulphur flakes and cleaned the surface. The free sulphur, however, did not deposit further. This was probably due to the formation of other compounds of sulphur such as H2S, S02, etc. which could have been removed from the solution due to the phenomenon of degassing. 

Exposure of ammoniacal silver chloride solutions to air or heat produces a black crystalline deposit of fulminating silver , mainly silver nitride, with silver diimide and silver amide also possibly present [1], Attention is drawn [2] to the possible explosion hazard in a method of recovering silver from the chloride by passing an ammoniacal solution of the chloride through an ion exchange column to separate the Ag(NH3)+ ion, prior to elution as the nitrate [3], It is essential to avoid letting the ammoniacal solution stand for several hours, either alone or on the column [2], See Silver nitride... 

The matrix compound is typically mixed together in an aqueous/ organic solution with the analyte, such that the relative concentration of matrix to analyte is on the order of 5000 or 10,000 to 1. The solution is applied to a surface that will be irradiated by the laser beam and the solvent is allowed to evaporate, leaving a solid, crystalline deposit of matrix and analyte. Many of the original applications described instruments in which the surface containing the dried matrix/ analyte sample was introduced into the vacuum housing of a mass spectrometer source housing for irradiation. However, recently it has been demonstrated that MALDI can be successfully carried out at atmospheric pressure (outside the vacuum chamber of the mass spectrometer), much in the same way as the ESI, APCI and APPI techniques. 

Adverse reactions occurring in at least 3% of patients include transient burning, stinging or discomfort upon instillation ocular itching/pruritus blurred vision dry eye tearing/discharge hyperemia crystalline deposits and foreign body sensation. 

CRYSTALLINE DEPOSIT OSTAINEO ST THE COOPERATION OF NUMEROUS ACTS OF IONIC DEPOSITION... 

Fig. 7.121. The formation of a crystalline deposit involving the deposition of several rows of atoms in a manner identical to that shown in Fig. 7.120.

Oxalic and Tartaric Acids. — On dissolving 1 gm. of citric acid in 2 cc. of water, and adding 10 drops of a 1 2 potassium acetate solution and 5 cc. of alcohol 85 per cent, no turbidity should be produced, nor should a crystalline deposit form within two hours. 

Ferric Orthoarsenite, FeAs03, was described by Reichard 9 as a rust-yellow powder obtained by adding potassium tetrarsenite to a dilute aqueous solution of ferric chloride. A substance of similar chemical composition has been found in a crystalline deposit formed during the Deacon process of making chlorine. The crystals of the pure salt are monoclinic, their crystallographic elements being 10... 

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