"Well, it's a good pump," replied Cole, defending his invention. "Wait until you see these," said Mr. Bergman, who had come to superintend unloading the engines. Each chemical apparatus consisted of a large copper tank on four wheels. It had a long hose, on a reel, and a rope to pull the machine by, similar to the old hand engine. But the principle of the new engines was entirely different. They shot a chemical stream at the fire, instead of one of merely water, and carbonous acid, or, as it is commonly called, carbonic acid gas, was generated. Fire will not burn where this gas exists, so that a small stream of the chemical was more effective than a big stream of water. The gas, being heavier than air, forms a sort of blanket over a blaze. In the big copper tank was placed water, in which was dissolved some bicarbonate of soda, the sort mothers use to cook with. Then, in a small receptacle, fitting in one end of the big cylinder, was some sulphuric acid, or oil of vitriol. The two liquids were prevented from mixing until the proper time, by a simple arrangement. When a fire occurred the chemical engine was to be hurried to the place. The hose would be unreeled, and then a lever and valve wheel would be turned, breaking the glass receptacle in which the sulphuric acid was held. This allowed the acid to mingle with the solution of soda water, and a strong gas was at once formed. The gas was under such pressure that it forced the combined soda and acid solution out through the hose for a considerable distance. It could be played on the fire, the gas would be generated, and the blaze would be extinguished in much less time than if water was used, and there would be less damage done. "Those are certainly fine engines," declared Bert. "I guess we'll have to have some practice with them before we'll know how to run them." "They are very simple in operation," said Mr. Bergman. "We'll arrange for some tests soon." "We ought to have a parade," suggested Vincent. "Let's take 'em through the town, and show the people what we've got." "A good idea," declared Mr. Bergman. "And, while we're about it, why not have a picnic." "A picnic?" repeated Bert. "Yes. Why not? Every village fire department has a picnic once a year. I don't see why Lakeville can't. It will stir the people up, and get rid of some of this jealous feeling." "I guess the boys would like it all right," replied Bert. "Then we'll have it over in Tillman's grove. I'll make the arrangements, and let you boys know when it's to be. Now we'd better get the engines into quarters."