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A study on white leather tannage

- Williams-Wynn, D A

Authors: Williams-Wynn, D A
Date: 1950
Subjects: Uncatalogued
Language: English
Type: Diploma theses , text
Identifier: http://hdl.handle.net/10962/193713 , vital:45389
Description: As has been noted in the previous section little or no complex formation occurs with either formate or acetate except possibly above pH 9*0 or so. These anions do not stabilise the aluminium solutions to precipitation - they may* however, be of value in controlling pH, as solutions of these salts buffer strongly in the region pH 4 to 5. The other salts, lactate, tartrate and citrate all show tendencies to complex formation though the degree to which this occurs varies with the anion. The complexes formed by lactate at high pH must be very unstable because on the addition of acid the pH corresponds to the calculated blank. Below pH 9.0 however, the curves deviate quite considerably showing that more acid must be added to reach a certain pH value than is required by the blank. This means complex formation has occurred with loss of -COGH groups. In this system too, buffering is apparent. The same is true of tartrate but this salt is not as efficient a buffering agent. This is probably due to the fact that the excess tartrate is not available as a buffer as it is precipitated as the acid salt which is only sparingly soluble. Citrate on the other hand must form very stable complexes, the effect of which is apparent at even very high pH values. In other words, addition of strong acid liberates free -GOGH groups which are immediately incorporated in the complex. This evidently does not occur with lactate or tartrate until lower pH values are reached. The ratio of lactate and citrate to aluminium appears to have some influence on the degree of masking as greater complex formation is found to occur at the higher ratio levels. Tartrate on the other hand apparently has a fixed complex forming capacity between 1 and 4 mols/mol aluminium, since the same deviation from the blank was observed irrespective of which ratio of the masking agent to aluminium, was employed. However, at ratios of less than 1 mol tartrate/mol aluminium, deviations from the blank were reduced and less stabilisation occurs as evidenced by the formation of precipitates containing aluminium under these conditions. In view of these facts it may be suggested that 1 mol tartrate combines with 1 mol aluminium to form a complex containing equimolar proportions of aluminium and tartrate. The effect of boiling apart from one or two exceptions always has the same effect, i.e. a shift to the acid side of the curve. Free acid must have been liberated which is an indication that olation might have occurred. In the lactate and citrate series dilution appears to reduce the complex forming capacity of these ions but tartrate is unaffected. Thus it would appear that the tartrate complex is more stable than those formed by lactate. Citrate stabilises aluminium solutions with fewer equivalents than tartrate, but the complex does not contain a constant ratio of masking agent to aluminium further quantities of tartrate cannot enter the complex even in the presence of large excess of the anion probably due to the effect of steric hindrance. , Thesis (Dip) -- Leather Industries Research Institute, 1950
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An investigation of certain complex ions of trivalent chromium by spectrophotometric and other physical methods

- Burley, Ralph Walter

Authors: Burley, Ralph Walter
Date: 1950
Subjects: Chromium
Language: English
Type: Thesis , Masters , MSc
Identifier: vital:4521 , http://hdl.handle.net/10962/d1014675
Description: Although chromium coordination compounds are of considerable technological importance, they have been subjected to few thorough investigations since Werner's original experlments, in spite of the fact that we now possess a number of accurate physical methods, not available in Werner's time for the study of coordination complexes, The object of the work described in this thesis was to obtain further information on the chemistry of complex chromium(III) ions with special reference to the dioxalato-diaquochromiate system, [Cr(C₂0₄)₂(H₂0)₂]. For this purpose; spectrophotometric and potentlometrlc measurements were combined to yield information on a number of topics, The spectrophotometric investigations consisted in measuring the absorption spectra of the potassium salts of the complexes under consideration and in observing the changes in light absorption which occur during their formatlon and decomposition. The instrument used was a Beckmann Quartz Spectrophotometer model du. More than than twelve new absorption spectra were measured in this work and in conjunction with the spectra of other chromium and cobalt complexes reported by earlier workers, these are used to review the position of spectrophotometry as a method of investigating chromium complexes. The reasons for the shapes of the absorption spectra are discussed and it is concluded that spectrophotometry is useful for observing the progress of reactions involving complex ions and for analysing solutions, but that more fundamental data cannot be expected from the absorption curves.
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Studies in the plant ecology of Fern Kloof near Grahamstown

- Seagrief, S C

Authors: Seagrief, S C
Date: 1950
Subjects: Plant communities -- South Africa -- Eastern Cape , Plant ecology -- South Africa -- Eastern Cape , Plants -- South Africa -- Eastern Cape , Forest ecology -- South Africa -- Eastern Cape
Language: English
Type: Thesis , Masters , MSc
Identifier: vital:4267 , http://hdl.handle.net/10962/d1014299
Description: The area studied at Fern Kloof, near Grahamstown, consists of a strip of vegetation approximately 260 yds. long and 50 yds. wide, in which there are two communities: 1) indigenous forest 2) exotic Pine forest (which has only one tree species Pinus pinaster). Throughout the thesis this species is referred to as the pine. The object of the investigation has been to determine whether these communities are natural or not. This has involved a study of the floristic composition, the life forms and the structure of the plant communities. In addition, various soil and environmental factors have been studied.
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