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May 23

Salts for hygrometer checking and calibration

I'm interested in using some salts to check and calibrate some humidity sensors for personal (rather than scientific or industrial use). I'm following the tutorial here: https://www.allaboutcircuits.com/projects/how-to-check-and-calibrate-a-humidity-sensor/ where it says that the salts should be wet to the consistency of wet sand. The article references some standard procedure but the standard procedure costs $50 to download. My question is, does it make sense to add water to the lithium chloride? It's meant to be bringing the RH down to 11.3% so it seems to me that adding water would impede its absorption of water from the air. Is the idea to have the salt partially, rather than fully, saturated with water, so it's kind of analagous to a buffer accomodating acids and alkalis? If that's the case, I'd still expect adding water to be unnecessary for that salt since the starting humidity is always bound to be higher than 11.3%, at least in my country (United Kingdom). If the lithium chloride was not stored in an airtight container, would it keep absorbing water from the air until it was no longer able to keep doing so? That would be another good reason to not add water before use; if it would prolongue its working life?

Also, how much salt is needed? Could 30 grams be enough to ready the air inside a 9 L food storage container? According to some online calculator, there are 40 grams of water in a cubic metre (1000 L) of air at 30 °C so... lets say your container was 100 L, you'd only need to absorb a maximum of 4 grams of water if you were going from 100% RH to 0% or give up 4 grams if you were doing the opposite. That doesn't help much because I don't know how much water 30 grams of lithium chloride can absorb (certainly less if I add some to it at the outset, though, right?).

Would sulphate of potash intended for gardening be likely to give the same result as reagent grade K2SO4? Apparently reagent grade only means ">95% purity" anyway.

The potassium sulphate gives an RH of 97-98% - this might be a stupid question but at that humidity, is there a higher risk of the water condensing on stuff inside the container? I was also thinking of using potassium carbonate (43%) and sodium bromide (58-60%) because 33% to 75% is kind of a big jump through the region that I expect most of the readings to be taken but then maybe I'm going a little overboard. --88.111.17.83 (talk) 04:16, 23 May 2020 (UTC)[reply]

The idea with these is that the standard humidity is created by a saturated solution, so you need some of the saturated solution of the salt. If your lithium chloride absorbed enough water to get to the consistency of wet sand, then you don't need to add extra water. Any way the lithium chloride solubility is high: 83.05 g/100 mL of water at 20 °C or 84.25 g/100 mL at 25° according to our article. So it is close to one for one in mass of water. And yes, i would keep absorbing water from the air if you did not keep it airtight. Fertilizer grade potassium sulfate is likely to have other soluble contaminants, perhaps potassium chloride, magnesium or sodium. There is no incentive to make it super pure, just safe enough. That will likely reduce the humidity from a saturated solution. Graeme Bartlett (talk) 22:44, 23 May 2020 (UTC)[reply]

Thanks very much, Graeme; this helps a lot. I think that water solubility value is exactly what I was looking for. I've found a fairly cheap supplier for all these salts so there's no sense in trying to skimp on the potassium sulphate. The lithium chloride is several times more expensive than the others. 88.111.17.83 (talk) 00:19, 24 May 2020 (UTC)[reply]

Plant

Hi, I would like to know what is the name of this plant:

--Red-back spider (talk) 11:24, 23 May 2020 (UTC)[reply]

Note that, according to the image’s uploader, the title and description state the wrong species. Brianjd (talk) 11:47, 23 May 2020 (UTC)[reply]

There is some difficulty in identifying immature foliage; my first thought was one of the birches, like this for example, but this hawthorn looks quite similar. Someone else might do better though. PS I took the liberty of resizing your image, feel free to reinstate it if you are offended. Alansplodge (talk) 12:09, 23 May 2020 (UTC)[reply]

It could also be elder, the first four or five leaves are not yet pinnate. Must wait one week more or so. 2003:F5:6F08:8200:705A:5DF6:6175:3EA0 (talk) 14:16, 23 May 2020 (UTC) Marco PB[reply]

Thank you. I think it is not a tree. The species mentioned are non-existent (or extremely rare) in that forest, and this seedling is common. I will upload more photos soon.--Pere Orga (talk) 19:27, 23 May 2020 (UTC)[reply]

It looks like a tree seedling to me, and does bear resemblance to Crataegus monogyna, or possibly another Crataegus, though here in the UK C. monogyna isn't usually a forest tree. It's not Sambucus nigra ("elder") - there's a pic of an elder seedling here, and it's quite different. Has the uploader not looked at the trees that are growing around the seedlings? If seedlings are plentiful in an area, it usually isn't too hard to find their parents growing nearby. Another place to ask would be at WT:PLANTS. PaleCloudedWhite (talk) 01:04, 24 May 2020 (UTC)[reply]

The plant could be one of these, but there just my guess:

@Brianjd: Yes, I know that the species name in the title is wrong, in fact the picture is getting deleted because of that and I want to save it. After all it can be used in an article. @Pere Orga: It might be a tree, Google says so but who knows, Google is right or wrong. --Red-back spider (talk) 05:33, 24 May 2020 (UTC)[reply]

@Red-back spider: I have outdented your entire comment so it is aligned correctly. My comment about the species name being wrong was for the benefit of other users. Brianjd (talk) 07:39, 24 May 2020 (UTC)[reply]

Hoheria ("lacebark") and Plagianthus regius are endemic to New Zealand, so seems less likely that there are lots of their seedlings sprouting in a forest near Barcelona. Crataegus laevigata might be a fit, at least better than C. monogyna anyway - these images of C. monogyna seedlings have more serrated leaves than the unidentified image. PaleCloudedWhite (talk) 08:06, 24 May 2020 (UTC)[reply]

More photos in the same forest. This ones of the same species:

Even if these have a different shape, I think this could be the same, too:

My opinion is that this is a liana, and that when it grows it becomes this one:

@PaleCloudedWhite: I have identified all the trees that grow in that forest (sorbus, pines, quercus, savinas, acer... and Fraxinus angustifolia and Celtis australis, but rare) and I have concluded that this is very unlikely to be a tree.--Pere Orga (talk) 22:24, 25 May 2020 (UTC)[reply]

Your "liana" pictures are a Clematis, though I haven't tried to ascertain which species. You could be right regarding the original seedling image - the seedlings of Clematis urophylla shown here, especially the slightly more mature ones in Image C, look quite similar. The images you took of seedlings with a different leaf shape are not the same as the original - I think they are Acer seedlings. PaleCloudedWhite (talk) 20:58, 25 May 2020 (UTC)[reply]

The only Acer I've seen growing there is Acer monspessulanum, seedling: https://commons.wikimedia.org/wiki/File:Aur%C3%B3_negre_(Acer_monspessulanum)_acabat_de_n%C3%A9ixer_-_Santa_Perp%C3%A8tua_de_Gai%C3%A0.jpg. I'll see how this one evolves too :) --Pere Orga (talk) 22:24, 25 May 2020 (UTC)[reply]