CIVIL TESTING

DETERMINATION OF NICKEL BY DIMETHYL GLYOXIME GRAVIMETRIC METHOD:

The quantity of nickel ions in a salt is determined by precipitation of the ions with dimethylglyoxime in an ammoniacal solution.  The product is an insoluble, red precipitate. The precipitate is collected and dried, and is then weighed.  Dimethylglyoxime behaves as a monobasic acid in the reaction. Precipitation is effected by the addition of dilute ammonium hydroxide, a hot solution of the nickel salt and dimethylglyoxime.  If manganese, zinc, magnesium or other alkaline earth ions are present, ammonium chloride must be added to prevent the precipitation of their hydroxides.

An alcoholic solution of dimethylglyoxime (DMG) is used as the precipitating reagent during the experiment because DMG is only slightly soluble in water (0.063 g in 100 mL at 25°C). It is therefore crucial to avoid the addition of too large an excess of the reagent because it may crystallize out with the chelate. It is also important to know that the complex itself is slightly soluble to some extent in alcoholic solutions. By keeping the volume added of the chelating reagent, the errors from these sources are minimized. The amount of the reagent added is also governed by the presence of other metals such as cobalt, which form soluble complexes with the reagent. If a high quantity of these ions is present, a greater amount of DMG must be added.

The nickel dimethylglyoximate is a precipitate that is very bulky in character. Therefore, the sample weight used in the analysis must be carefully controlled to allow more convenient handling of the precipitate during transferal to the filtering crucible. To improve the compactness of the precipitate, homogeneous precipitation is often performed in the analytical scheme. This is accomplished by the adjustment of the pH to 3 or 4, followed by the addition of urea. The solution is heated to cause the generation of ammonia by the hydrolysis of the added urea A slow increase in the concentration of ammonia in the solution causes the pH to rise slowly and results in the gradual precipitation of the complex. The result is the formation of a more dense, easily handled precipitate. Once the filtrate has been collected and dried, the nickel content of the solution is calculated stoichiometrically from the weight of the precipitate.

SILICON – GRAVIMETRIC METHOD:

Gravimetric method is widely used in chemical analysis of metallic material. For some element, such as Si, Mo, Ni, Zr, quantitative gravimetric analysis are typical and traditional method. Balance is a fundamental instrument in the gravimetric method. Through the mathematical model, we can find that all the input quantities are related to the balance.

Sample is decomposed with hydrochloric and nitric acids. The acid solution is heated and evaporated into dryness. Silica is separated as insoluble SiO₂xH₂O, filtered off. The filtrate is evaporated to dryness and ignited in a platinum crucible at 1050°C, weighed. The residue is treated with hydrofluoric and sulphuric acids, Silicon is volatilized as silicon tetra-fluoride and the impurities are left as sulphates residue, the crucible is weighed. The loss in weight represents the amount of silica.

STAINING TEST FOR MASONRY CEMENT:

Surface preparation is one of the most important steps of the staining process. The brick or masonry surface must be free of debris, dirt and oils.

Process – The stain mixes with the substrate (brick, block, stone, cement etc) to force a chemical reaction, which changes the color of the surface, similar to a forced bond.

Application – The appearance of the finished product is very much influenced by the manner in which the stain is applied. The stain can be sprayed, mopped, brushed, rubbed etc.