The heading of this chapter must be seen to "beg the question," inasmuch as it leads to the assumption that a coagulant (in the popular sense) is necessary to secure coagulation. In point of fact, methods are sometimes employed which depend upon no artificial coagulant to produce the desired effect. To these methods reference will be made later. In this section it is proposed to describe briefly the more important agents which are used, or might be used, in effecting coagulation. In the class of those which are not in common use some could be used as expedients, while others are only of scientific interest. ACETIC ACID.--There is no need to enter into a discussion of the merits of this agent. In practice it remains the cheapest and safest coagulant known at present. FORMIC ACID.--This agent is equally as safe to use as acetic acid, and as easy to handle. Bulk for bulk its coagulative power is higher than that of acetic acid. Its pre-war shipping price, when taken in conjunction with its coagulative power, was slightly below that of acetic acid, but local prices put the balance in favour of the latter. If prevailing costs put it on terms of parity with acetic acid, there would appear to be no reason why formic acid should not have a widely-extended use on plantations. CITRIC ACID, TARTARIC ACID.--The acids of the extracted juices of most tropical fruits consist, to a large degree, of citric or tartaric acids. These can be used in place of acetic acid as satisfactory coagulants in case of emergency; but the questions of availability of supplies and of costs preclude their more general adoption. OXALIC ACID.--This is a satisfactory coagulant as far as observed effect is concerned. It produces a rubber paler than ordinary coagulants (without the use of sodium bisulphite), as it has the nature of an anti-oxidant. It would not be a safe agent in the hands of coolies, as it is classed as a poison. SULPHURIC ACID.--During the War, in a period of shortage of acetic acid and of high prices, this agent was used with success on some estates. It scarcely need be remarked that it is a dangerous substance to handle, and that its employment must be accompanied by close European supervision. At prevailing prices during the War it was very much cheaper than acetic acid, and even at the present reduced cost of the latter the advantage still lies with sulphuric acid. It must be emphasised, however, that the abuse of this agent to any but the slightest degree is harmful to the resultant rubber. Hence its use would be sanctioned _only in the absence of the commoner, and much safer, coagulants_. In view of the possible incidence of such an emergency, the following notes are given. It is impressed that strict adherence to the rules must be given. HANDLING SULPHURIC ACID.--(_a_) Always use glass or glazed earthenware vessels.