We have received a letter from our correspondents, Parsons Hoig, of Jacksonville, Fla., in which they state they have been put to their " trumps" to account for explosions taking place in their steam boilers when there is an abundance of water in them, even "reaching to the upper try-cocks." They have a mill at the mouth of the St. John's river, and have sunk a tank in the sand to obtain fresh water for their steam boilers. In rainy weather they can obtain a sufficient supply of this, but during droughts they have to take salt water by a pipe from the river, and it is this water which is the cause of explosions. They have had three explosions in boilers ; one five years, one eighteen months ago, and the other about the middle of April last. The boiler that burst latterly was thrown fifty feet into the air ; everything in its vicinity was a complete smash—it was, in short, a young earthquake. Mr. Parsons says he has come to the conclusion that there must be some substance in the water which produces an explosive gas. Our opinion is different from that of Mr. Parsons. Even allowing a gas to be generated in the boiler, it would not explode with* out being ignited, and this could not be done if the boiler had plenty of water in it. The boiler may have been priming when the upper cock was tried, and some water would flow out of it, although there was actually not a sufficient quantity to cover the flue lines. A deficiency of water, with an excess of steam pressure, may really have been the cause of these explosions. Such waters are also very liable to form incrustations, and if there were a thick scale formed in this boiler, it might have been displaced when working, and the overheated metal coming suddenly in contact with the water, a great supply of steam may have been rapidly generated, and thus have caused the explosion. But whatever may have been the cause of these boiler explosions, we cannot attribute them to anything in the water. We believe that any steam boiler in the same situation if blown off frequently, cleaned out every two weeks, and strict attention paid to have plenty of water in it while working, will not explode, provided the pressure is not carried too high.