“Not now.  It used to be a notion that an iron skin damaged the cargo; so the first iron ships were ceiled with wood.”

“Are there any drains in the ’tween-deck to let water out, in case it gets into that deck from above—­a sea, for instance?”

“Yes, always; three or four scupper-holes each side amidships.  They lead the water into the bilges, where the pumps can reach it.”

“I found up there,” continued the doctor, “a large piece of wood, badly charred by acid for half its length, charred to a lesser degree for the rest.  It was oval in cross section, and the largest end was charred most.”

“Scupper plug.  I suppose they plugged the ’tween-deck scuppers to keep any water they might ship out of the bilges and away from the lime.”

“Yes, and those plugs remained in place for days, if not weeks or months, after the carboys burst, as indicated by the greater charring of the larger end of the plug.  I burrowed under the debris, and found the hole which that plug fitted.  It was worked loose, or knocked out of the hole by some internal movement of the broken carboys, perhaps.  At any rate, it came out, after remaining in place long enough for the acids to become thoroughly mixed and for the hull to cool down.  She was in the ice, remember.  Boston, the mixed acid went down that hole, or others like it.  Where is it now?”

“I suppose,” said Boston, thoughtfully, “that it soaked up into the hold, through the skin.”

“Exactly.  The skin is calked with oakum, is it not?” Boston nodded.

“That oakum would contract with the charring action, as did the oakum in the hatch, and every drop of that acid—­ten thousand gallons, as I have figured—­has filtered up into the hold, with the exception of what remained between the frames under the skin.  Have you ever studied organic chemistry?”

“Slightly.”

“Then you can follow me.  When tallow is saponified there is formed, from the palmitin, stearin, and olein contained, with the cauticizing agent—­in this case, lime—­a soap.  But there are two ends to every equation, and at the bottom of this immense soap vat, held in solution by the water, which would afterwards be taken up by the surplus lime, was the other end of this equation; and as the yield from tallow of this other product is about thirty per cent., and as we start with eight thousand fifty-pound kids—­four hundred thousand pounds—­all of which has disappeared, we know that, sticking to the skin and sides of the barrels down here, is—­or was once—­one hundred and twenty thousand pounds, or sixty tons, of the other end of the equation—­glycerine!”

“Do you mean, Doc,” asked Boston, with a startled look, “that—­”