In making an Oolong Black tea, which occupies an intermediate position between Green tea and Black Souchongs and Congous, the leaves are first exposed to the action of the air for a considerable time, and in many cases, to the sun also. An incipient fermentation may take place, although this is denied by some. There is certainly a chemical change beyond the brief preliminary drying of Green tea. During this period the leaves (in China) are stirred and tossed by the hands. The effect, if not the object, is to expose greater surfaces to the air, and to increase oxidation. It is during this operation that the leaves first begin to manifest characteristics of manufactured tea, in the way of a fragrant tea odor which the green leaf did not possess. The development of sweet odors in new hay, quite different from those of green grass, and also the artificial development of flavor in tobacco leaves, may be recalled in this connection. This prolonged exposure to the air is termed "withering," and the leaves become soft and flaccid, as they do in the first artificial heating for Green tea. In withering, the leaves lose about one quarter of their weight in moisture. The leaves must not be bruised before the termination of this treatment, or injurious chemical changes will begin. The second operation with Black tea is the same rolling into balls, twisting and squeezing, as in Green tea. Mr. Crole says that the sap of the leaf thus liberated from its cells "is spread all over the surface of the rolled leaf, where it is in a very favorable position for the oxygen of the atmosphere to act upon it during the next stage of manufacture, namely, fermentation." Fermentation, he regards as an oxidation process mainly. For the "fermentation" stage, if that controverted term correctly designates the process, the rolls are either left undisturbed to heat, or, as in Indian methods, the rolls are broken up, and the leaves distributed in drawers, with free access of air. In either case, a spontaneous heating follows, and chemical action is indicated by a change of color which reddens and darkens the leaf, and by the evolution of further pleasant "tea" odors. Some of the tannin is said to be converted into glucose. Care must be taken, Mr. Crole says, to arrest fermentation at the proper stage by the first "firing," and this firing expels about half of the remaining moisture of the withered leaves, and probably develops an additional portion of those volatile oils which give fragrance and taste to manufactured tea; and which Mr. Crole designates by the name of "theol." Too high or too long continued firing drives off these oils with the watery juices. They are also wasted by exposure of manufactured tea to the atmosphere. Firing is sometimes divided into two or three stages. In the above summary we have described all essential treatment of tea leaves necessary to produce manufactured tea.