In our description of the novel steam boiler, published on page 209, last volume, we made a quotation from several eminent writers and experimenters on the subjects of heat and steam, to the effect that the tubular system in steam boilers was wrong in theory and unsafe in practice, and although this system has hitherto been extensively used on account of some advantages which it secures, it has long been a serious question with thinking men whether these advantages were not obtained at too dear a rate.

While not prepared to admit all the force of the objections made to the tubular system, there are arguments against it that it will not do to treat lightly and which seem to us more and more forcible the more we candidly reflect upon the subject. One of the most forcible of these which occurs to us is, that in the tubular system the disruptive force of unequal expansion is far more likely to become a cause of danger than in the plain cylinder boiler. In such boilers the tension of expanded tubes is transmitted to the shell, which are greatly strained without doubt, often nearly to the verge of rupture. When this occurs it is evident an unusual strain, caused by sudden generation of steam, would act in concert with the expansion of the tubes, and we have no doubt these causes combined have given rise to many an explosion when the steam, acting singly, could never have produced rupture.

But while we give due weight to this argument, there is one often referred to by our correspondents, and which we often see stated in newspapers, as ridiculous as the one we have noticed is forcible. It is that when, in such boilers, water, by carelessness or otherwise, is allowed to fall below any of the tubes, the steam which surrounds them is decomposed, and becomes an explosive mixture of hydrogen and oxygen gases, ready to explode with terrible violence whenever the temperature of the tubes shall have reached the proper point.

This argument is ridiculous, because it rests on no experimental basis. It is a flimsy theory, entirely unsupported by any facts. Never has it been proved that hot iron, at any temperature likely to be obtained in steam boiler tubes, decomposes steam except by itself appropriating the oxygen of the steam, and leaving the hydrogen, by itself no more explosive than any other heated gas.

The sole object of the tubular boiler is to increase the heating surface, without corresponding increase in other particulars. That it is not the only means whereby this object can be secured has already been demonstrated and we believe will hereafter be shown in divers ways. We have no more doubt that the next fifty years will witness the total abandonment of the tubular system, than we have that the world will last that length of time.