跳到主要內容

發表文章

冬至

2024年12月21日17时21分 冬至日係北半球全年白晝最短,夜晚最長的一日 圭表:正午日影最長。 從冬至到下一個冬至的時間稱為一「歲」,而從農曆正月初一到下一年正月初一的時間稱為一「年」。 冬至,阴极之至,阳气始生,日南至,日短之至,日影长之至,故曰“冬至”。 【古人的新年】冬至是二十四节气中最早制订出的一个,早在上古时期,中国人就已经用土圭观测太阳,测定出了冬至。古人认为自冬至起,白昼一天比一天长,阳气开始回升,代表下一个循环开始,是大吉之日。 人们最初过冬至节是为了庆祝新的一年的到来。据记载,周秦时代冬十一月为正月,所以 贺冬与拜岁相同 ,并没有分别,人们以冬至为岁首过新年。直到汉武帝采用夏历后,把正月和冬至分开,从此人们开始专门过“冬至节”是自汉代以后才有,盛于唐宋,相沿至今。 Reference: Ytliu0   Weixin
最近的文章

Moon phases of 2025

 Calendar form( in BJT UT+8) Text form Reference: Weixin

pH meter - How it works

 Glass electrode

天水圍日落

 日本風格 from littlepig: From sun locator app:

Achieve mash pH using Phosphoric acid

Brunwater calculator work best for me. Work by dilution, ie to lower acidicity,( higher pH values) step by step Do by making 350 ml then dilute to 3500 ml(target) Sanity check: Rinse ph meter with water when pH readings is doubtful. Measure again with  tap water, and calibration liquids From experience, initial 350ml is around pH 2.5 or 2.6 When making 3500 as final volume, start by add 80% to 85% of calculated water amount, ie 2800 ml in this case Add the required salts, eg gypsum and calcium chloride before adding more water. Stir to make sure all is dissolved  Add 50ml every time to watch how pH values go up ( less acidic) PH starts ~ 4.6 to 4.8 Every 50 to 100 ml lower acidicity by ~0.1(pH values go up 0.1) The trend is not linear,but increase in steps  I think ph 5.4 or 5.5 is good enough. My cheap pH meter can have a deviation of 0.2 or maybe more. Double check with ph paper when reaching ~5.0 Tips Constant stirring  Read after 15 seconds Cleanse the pH meter ...

Gypsum 石膏粉

CaSO4 · 2H2O. Dihydrate  生石膏粉 现在药房出售的生、熟石膏均为白色的粉末状,不太好鉴别。简易的区分方法为:取石膏粉末10克,加水约15毫升,搅拌均匀。 放置10分钟后,若呈干性黏团块状者是熟石膏,而呈湿性散渣状者,则为生石膏。 硫酸钙化学式CaSO4。熔点1450℃,相对密度2.96,难溶于水???。它的二水合物CaSO4•2H2O俗称石膏(或生石膏)二水硫酸鈣。 gypsumchina 半水合物CaSO4•1/2H2O hemihydrate称熟石膏(或烧石膏)。(TB 最常買到的是熟石膏,甚至把熟石膏當作生石膏賣)plaster of paris. 二水 vs 無水 石膏加热至128℃,失去大部分结晶水,变成熟石膏;163℃以上,结晶水全部失去。熟石膏粉末与水混合后有可塑性,但不久就硬化重新变成石膏。此过程放出大量热并膨胀,因此可用于铸造模型和雕塑。 硫酸钙和石膏可用作联合制造硫酸和水泥的原料,还可做油漆的白颜料、纸张的填料 熟石膏粉用作豆腐的凝结剂。 Gypsumchina Gypsum is moderately water-soluble (~2.0–2.5 g/L at 25 °C)and, in contrast to most other salts, it exhibits retrograde solubility, becoming less soluble at higher temperatures.  When gypsum is heated in air it loses water and converts first to calcium sulfate hemihydrate (bassanite, often simply called "plaster")  and, if heated further, to anhydrous calcium sulfate (anhydrite).  As with anhydrite, the solubility of gypsum in saline solutions and in brines is also strongly dependent on sodium chloride (common table ...

行星天象圖 Celestial phenomena 2025

 From NAOJ : HKT(UT+8) From HKO