Dyestuffs basic, charge

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. 

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