In Little House in the Big Woods (Chapter 2, “Winter Days and Winter Nights”), Laura Ingalls Wilder wrote:
Ma sat in her rocking chair, sewing by the light of the lamp on the table. The lamp was bright and shiny. There was salt in the bottom of its glass bowl with the kerosene, to keep the kerosene from exploding, and there were bits of red flannel among the salt to make it pretty. It was pretty.
I thought about this today as I put my empty glass lamp on display. Back before the move, it was filled with lamp oil, which is kerosene that has been more refined than it was back in Laura’s day, to reduce both the soot and the smell. Because my lamp was part of my “Little House” collection, I had added a handful of coarse sea salt and some bits of red flannel. It always surprised me that the red dye from the flannel never tinted the oil, nor did the salt dissolve.
From time to time, people in one LIW group or another have discussed how the salt could have kept the kerosene from exploding. From time to time, I’ve researched it and I still haven’t a clue.
In the mid-19th century, naturally occurring petroleum was separated into three main components – naphtha (which includes gasoline and benzene), kerosene, and paraffin oil – according to their boiling ranges. Naphtha boiled at a lower temperature than kerosene, and the more naphtha in the mix, the more your lamp would sputter. It might even explode. Everything I read tells me that pure kerosene does not explode, so the “kerosene” people put in their lamps might be any range of purity, something that you just had to take the seller’s word for back then.
I spent a lot of time looking at old newspapers tonight, and kerosene lamps sure did seem to explode a lot. And burn down houses. And kill people.
One hundred parts of crude petroleum would yield 16.5 parts naphtha, 55 parts kerosene, 19.5 parts paraffin oil, and other coal-oil products. The difference in these by-products was not in kind, but in degree. The difference in naphtha and kerosene was a perfectly arbitrary one; the difference is that naphtha is a little more volatile and inflammable than kerosene, meaning that it doesn’t burn as well as kerosene, but it explodes more readily.
In those days before automobiles, the naphtha part of petroleum was pretty much considered worthless (3 or 4 cents per gallon), and refineries tended to burn it off to provide heat, rather than hang onto it. But the more naphtha they were able to sneak into the more desirable stuff called kerosene, the more waste was avoided and the more profit realized.
Apparently, it’s the vapor from kerosene that will ignite. So a filled lamp tended not to explode as often as a lamp low on kerosene. And the more naphtha in the mix, the lower the temperature at which the explosion might take place. Of course kerosene lamps get hot; just touch the area around the burner of one when it’s lighted.
Now for the salt. If it’s the vapor (and apparently you need just the right amount of air) that ignites and explodes, uh, the salt is lying there on the bottom of the lamp and not anywhere near the vapor, right? In fact, laboratory sodium (not salt) is often stored in kerosene, and the United States Strategic Petroleum Reserve (688.5 million barrels of crude oil as of December 1, 2006) is stored in salt domes below the Gulf of Mexico.
And I still don’t know how the salt kept the kerosene from exploding. Or even if it did.
