Last fall, the Slominski and Lawton families of Garner, North Carolina were vacationing in a remote area of Cape Lookout National Seashore when they noticed small objects bobbing in the surf. They collected a few of the items, and for roughly thirty minutes many more examples of the same item continued to float by. Not knowing what they were, they limited their collecting to about fifteen pieces. The items gathered were delicate glass tubes with a thin tube at the top containing a graduated paper scale, with a larger air-filled chamber at the middle, and a small bulb at the bottom filled with little lead pellets held in place by a cotton plug.
During the recovery, one of the fragile items fractured and from it they recovered a paper scale with the words “Sea Water G. Tagliabue New York.” Despite seeing what they described as a “hundreds” of the items in the surf, when they walked down the beach to see how many had washed ashore they couldn’t find anything—no complete pieces, no broken glass, no loose paper scales…nothing. It was as if the bobbing items had simply vanished into thin air.
They showed the items to volunteers and staff working at Cape Lookout and were told that cargo and other items from the hundreds of shipwrecks that surround Cape Lookout regularly washes up on area beaches. While storms or rough seas may wash heavier cargo from the wrecks, sometimes it’s the decomposition of the ship structure or crates within it that allows trapped items to escape.
Once home, Mark Slominski began trying to identify the items. After a little research he was pretty sure what the family had recovered was some form of hydrometer, but he wasn’t sure. He contacted several naval historians to try and gain additional insight into the instrument, but they couldn’t provide any assistance.
Eventually, Mark contacted the Scientific Instrument Society and joined the RETE mailing list (a mailing list devoted to the history of scientific instruments) operated by the Museum of the History of Science at Oxford. After posting a query to the list serve, members Sara Schechner (David P. Wheatland Curator of the Collection of Historical Scientific Instruments at Harvard) and researcher Julian Holland suggested he contact the Mariners’ Museum for additional assistance. In late January, Mark’s request for help reached me. Images of the items and the word “sea water” on the paper scale immediately told me the instruments were most likely salinometers, a type of hydrometer that’s specifically designed to measure the amount of salt in a marine steam engine boiler.
I was aided by the fact that we have a number of fragmentary instruments recovered from the engine room of the USS Monitor in 2002. Despite being broken, several paper scales from the Monitor instruments survived and at least one showed it was by the same maker as those recovered by the Slominski and Lawton families: Giuseppe Tagliabue (1812-1878) of New York.
Confusing the situation was the fact that Tagliabue marked one of the scales with the words “Sea Water Hydrometer,” while one recovered by the family was marked “Salinometer for Sea Water” and yet another was simply marked “Sea Water.” Holy moly dude—could you have been a little more consistent???
Of course this raised questions: Is it a salinometer or a hydrometer? How do you tell the difference between those two instruments? Is a “sea water hydrometer” different from a “salinometer for sea water” or are they just named differently but used for the same activity? I had no freaking clue.
You guys know me, I am definitely not one to let a sleeping dog lie. It became a total obsession to answer all of the questions that were now bobbing around in my head. I am happy to say, that after reading a bit about marine steam engines and boilers I think I have finally sorted things out—at least enough to visually tell the difference between a hydrometer and salinometer (which is technically still a hydrometer but let’s ignore that!).
Hydrometers are meant to measure the specific gravity of a liquid so they carry a uniformly graduated scale that helps determine the density of the liquid. Since there are obviously about a zillion different types of liquids, there are many different types of hydrometer. A hydrometer that measures the purity of milk is called a lactometer. A hydrometer that measures the alcoholic strength of a liquid is called an alcoholometer. A hydrometer that measures the specific gravity of an acid is an acidometer. You get the idea. There is one drawback with using a hydrometer to measure salt content and that is you must also have a barometer present to determine atmospheric pressure. To get around this problem a combination of the two instruments was created: the salinometer.
Salinometers are specifically designed to tell a marine engineer the portion of salt in his boiler water. Why do they need to know this? Well, too much salt means it takes more fuel to bring the water to a boil. It also leads to scaling inside the boiler which could cause the boiler to fail thanks to overheating (it’s more technical than that but that’s the gist of it). The scale inside a salinometer is set for the range of boiling points for salt water (190°F to 210°F) with additional graduations for 1/32, 2/32, 3/32, etc. to show the portion of salt in the water. Those graduations tells the engineer when it’s time to replace too-salty water with less-salty water. The scale is marked “blow” which means it’s time for the engineer to open the valves that allow the steam inside the boiler to “blow off” the salty water so fresher water can be drawn in.
Learning all this helped me understand why identical instruments seem to have multiple terms describing them. Tagliabue’s identification of the instrument in the USS Monitor collection as a “sea water hydrometer” is actually a salinometer. Likewise, the fragmentary scale that only has the word “water” remaining—but shows the 190°F to 210°F temperature scales is also a salinometer.
After sorting all this out, I am happy to say that the Slominski and Lawton families graciously donated not one but TWO of the salinometers they recovered and the loose paper scale from the broken instrument. This wonderful donation gives us examples of one of the earliest forms of salinometer used on board a steamships. It’s also great for our visitors because it will allow us to display a complete example by Tagliabue next to a fragmentary instrument which will give them a much better understanding of exactly what the whole instrument looked like.
For the Slominski and Lawton families, they can revel in the fact that they were able to save so many these amazingly delicate and rare instruments (from the aspect of dating and manufacturer) from destruction and know that thanks to their efforts they will be preserved for the benefit of future generations.