Mutual precipitation

Dispersions to be added to latex must have good storage stabiHty and be compatible with the latex the pH of each should be similar to that of the latex, eg, pH 8.5—11 for ammonia-preserved latex and pH 3.5 for cationic-preserved concentrates. Addition of low pH materials to high pH latex or vice versa generally results in mutual precipitation and coagulation of the suspended mbber particles. 

If both silica and magnesium are present, they mutually precipitate thus, salts of either mineral may be added to the BW to provide a balance and ensure coprecipitation as serpentine ... 

Mutual precipitation of oppositely charged dye-stufifs is the basis of a number of volumetric processes of estimation thus the evaluation of tannin solutions may be accomplished with night blue or of eosine with night blue. 

The polyanion-polycation complex (symplex) formation process is a phenomenon that had long been known on an empirical base from the mutual precipitation of proteins [150]. The internal structure and the properties of the resulting complexes are strongly influenced by the nature of the polymeric components and the system conditions. The polymer parameters include the molar mass, the... 

Consequently, the fractionation of heterogeneous polymers by the method of fractional precipitation mostly effects sharp, quantitative separations. Although, as a rule, chemically dissimilar polymers cannot be combined in one solvent since they will mutually precipitate each other, starch affords an example of the few exceptions to this rule, as its aqueous solutions actually contain two chemically dissimilar polymers, namely, amylose and amylopectin. Nevertheless, until 1950, there were no reports of any systematic studies on the effects caused by the gradual addition, to aqueous, starch dispersions, of water-soluble substances possessing non-solvent character for whole starch. Likewise, no work seems to have been done on establishing the relative difference in solubility between amylose and amylopectin in binary solvent mixtures. ... 

Basic dyes, being cationic, can, under certain conditions, be precipitated by direct or acid dyes which are anionic. The two, therefore, cannot be used together except at very low concentrations. Advantage can he taken of this mutual precipitation because the direct dye acts as a mordant when on dyed cellulosic materials and, therefore, basic dyes can be used for after-treatment to brighten shades. 

The method of application is to make up a bath with 3 per cent on the weight of the goods of ammonium acetate and the dye. The goods are entered and the temperature is raised to the boil during twenty to thirty minutes and dyeing is continued for a further 45 minutes. If a two-colour effect is desired the basic dye must be added to the dyebath ten minutes after the acid dye. For shading, the temperature must be lowered to 70°C (158°F) and, to avoid mutual precipitation in concentrated solutions, the acid and basic dyes must be added separately. 

Another effective method of bringing about precipitation is by mutual cancellation of charges. This can be done by adding a negative suspensoid to a positive suspensoid or ice-versa. This is also known as mutual precipitation of colloids. 

In accord with their limits of identification and the corresponding dilution limits, spot reactions can be applied directly only within certain concentration ranges of the material to be detected. When higher dilutions are presented, preliminary concentration is essential. Evaporation of considerable volumes of liquid was formerly employed almost exclusively, but this has been replaced in many instances by the use of so-called "collectors". The latter are solids which have the ability to fix on their surface traces of the sought material. The action of collectors is due to the formation of mixed crystals in some cases, or to mutual precipitation, or adsorption. Traces accumulated from highly dilute solutions by these gathering aids can then be tested directly on the collector by suitable spot reactions, or the gathered material may be put into solution in a small volume before the test is applied. 

Test by mutual precipitation of zinc and cobalt with mercury thiocyanate ... 

In the presence of iron salts, red soluble ferric thiocyanate is formed and interferes with the discernment of the blue mutually precipitated mercurithiocyanates. In this case, the mixture should be treated with a few milhgrams of alkali fluoride, one or two minutes after the addition of the reagents. The red color due to the ferric thiocyanate disappears, because of the production of colorless [FeFe] ions. 

Biltz found further that where acid and basic dyestuffs had opposite charges and were mutually precipitated, the formation of an insoluble chemical combination could be assumed. This corresponds to what is known of acid and basic dyestuffs in the state of crystalloids namely that they unite, and when the combination is insoluble a precipitate is of course formed. Doubtless such reactions occur in the case of many dyestuffs. The more colloidal the character of these dyestuffs the more nearly will the laws of colloidal reaction obtain. Moreover Biltz has pointed out that with colloids of the nature of gold such chemical reactions are not possible. Nevertheless colloidal gold is precipitated by positively charged dyestuffs. The cause is doubtless the neutralization of the charge on the particles. For further particulars attention is called to Chapter XI. 

Very interesting also is the experimental result obtained by Doer-inckel in regard to the relation of the concentration of the two components in the mutual precipitation of colloidal silver (Argoferment,... 

The second method is the opposite of the first that is to say, the potassium bromide solution is in the buret and is added to the solution of silver nitrate. The phenomena are quite analogous, but the hydrosols differ in one important particular. In the first case as long as the halide ion is in excess of the silver, the ultramicrons are charged negatively, while in the second case where the silver ion is in excess the ultramicrons are charged positively. The two halide hydro-sols mutually precipitate each other, as is to be expected from a mixture of oppositely charged colloids. 

Polyanion-polycation-complexes are known for a long time on an empirical basis from the mutual precipitation of proteins. Already at the end of the previous century Kossel [1] recognized the electrostatic interaction between the oppositely charged polyions as the driving force for precipitation. Willstaetter [2] also introduced the term symplexes for polyelectrolyte complexes. 

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