Drying tubes are pretty basic standard piece of kit for any lab that will ever deal with reagents or reactions that involve anything water sensitive, they plug into a female joint of glassware where it is open to the air and cannot be plugged due to factors like heating, or high vapor pressure of something inside, so they need to be equalized with external atmospheric pressure, as stoppers would get pushed out, or worse, fired out, so rather than sealing all holes off with stoppers, a drying tube is used, a wad of something suitable to contain the dessicant is packed at the end near the bulb, to stop it falling into the reaction flask, such as cotton wool, wire wool if its anything nastier, or whatever, so long as its permeable, will hold, and not get melted, set on fire etc. by the drying agent
(things like phosphorus pentoxide for instance, one of the most powerful dessicants available, the acid anhydride of orthophosphoric acid, H3PO4, is extremely acidic and generates a LOT of heat when it hydrates, but for things that aren't acid sensitive, or just for keeping atmospheric moisture from entering when it absolutely has to be kept dry, such as for example, with a LAH reduction
(lithium aluminium hydride, powerful reducing agent, but it has to be used in freshly flame-dried glassware, thats just come out of the oven after cooling down (since it needs using in an etherial solvent usually, most commonly THF [tetrahydrofuran], although diethyl ether, diisopropyl ether etc. can also be used. Reduces nitro, nitrile, amide, oximes, azides and imines to amines, as well as esters, carboxylic acids, carboxylic acid chlorides (and presumably also acid iodides and bromides although very unlikely to reduce an acyl fluoride, although the latter I'd rather not be around as many of them would present the danger of forming a lethal and nigh untreatable metabolic poison, fluoroacetate/fluoroacetic acid, which is extremely unpleasant stuff, gets metabolized like acetate via the Kreb's cycle and to fluorocitrate, where citrate is meant to be there,
during the metabolic generation of ATP, the cellular energy 'currency' since the tight carbon-fluorine bond cannot be split off by aconitase [no relation to the plant aconite, or monkshood/wolfbane], its the equivalent of throwing a metabolic spanner into the gears and it just binds and clogs the enzyme, starving cells of energy and killing them, toxic to pretty much every living thing, near irreversible, certainly with what hospitals have access to, and targets the organs especially with the highest energy demands, such as heart and brain. As toxic as many battlefield nerve agents if not more so than some of the entry-level ones like sarin and tabun, and in any case, all of them would hydrolyze easily to give off fumes of hydrofluoric acid which itself is pretty foul stuff).
LAH also reduces C=O bonds in ketones and aldehydes, in the case of C-N, C=N or azides giving amines, in the other cases giving primary alcohols. Its pyrophoric though and careful drying of glassware fresh before use is needed, since it reacts violently with water, with wet solvents (the THF/ether should be freshly distilled immediately before use over lithium or sodium metal, although one could use calcium, barium or strontium for it if thats whats to hand, and a blanket or flow of inert gas such as a helium or argon atmosphere must be used with it too. Tends to scare the pants off inexperienced chemists their first time around with it due to its reputation. But it is clean, and its certainly effective. For things like nitro compounds to amines it'd be my first choice, unless the substrate is very expensive or has other functional groups it won't be selective with, in which case I'd probably use Red-Al, despite the price ( sodium bis(2-methoxyethoxy)aluminium hydride ), which is pretty selective, quite gentle on substrates, not pyrophoric, and generally one of the best of the hydride reducing agents for sensitive substrates, but the catch is, you need 7 molar equivalents of Red-Al per mole of substrate to be reduced, assuming there is only one functional group to be reduced on the molecule, and its damnably expensive.
I need to get some though, for one particular project, since the substrate in question, there are two of them to be created from just 5g of the initial precursor to both, I doubt I could buy more, and the chemistry would be very difficult most likely and involve a lot of purification via column chromatography, vacuum distillation and such of crude product that'd almost certainly be a mixture, I only have the 5g of the starting compound, thankfully only a two-step reaction plus cleanup, but all the same, it cost me £80-something for the 5g and making it would be a certifiable nightmare, meaning every scrap needs to be made as good a use of as possible and the best possible reagents for every step, and best quality of same forked out for and my wallet being made to ache yet further in the process.
These came for me the other day:
Microscale integrated pear-shaped flask with side-arm, vigreaux column and vertical+sideways arms for reflux and distillation
And a pressure-equalized addition funnel, for additions in closed-circuit systems. With a normal separatory funnel being used as an addition funnel the top has to be open to the air because as liquid drains out into wherever its going, the air pressure difference created when it does cannot equalize and the liquid in the funnel gets 'stuck', the pressure-equalized addition funnel allows gas exchange through the side tube between the underside of the stopcock and the main body of the funnel, with a limited amount of gas, such as an inert atmosphere, that remains constant and just cycles round keeping the pressure normalized and allowing flow to continue. Rather handy little piece of equipment, I've wanted one for a while and finally, during my last lab glass update, spotted one on ebay for around £15 give or take a couple of quid. a 100 pack of capillary tubes came as well, won't bother to take a photo of those however, as they are nothing particularly interesting to look at, just very thin-bore, thin-walled single-use soda-lime glass tubes a few inches long, about 1mm ID, for taking the melting point of a sample, heated slowly, temperature monitored with a thermometer, the tube going into the solid sample, and when it melts the narrow bore causes a portion of sample to flow up into the tube by capillary action, impurities in the sample generally depress the melting point. Tested something I was working on last night and it was off by 14-16 degrees 'C, letting me know that I need to wash it first with dilute acid, then water, followed by dissolving it in hot alcohol and further washing with sodium bisulfate solution to remove unreacted starting reactants and catalyst. Nothing terribly difficult, just boring and more effort, but easier to clean up now than after the final reaction in the series of steps between start point and desired end product.
